1ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin/* 2ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. 3ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 5ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * This code is free software; you can redistribute it and/or modify it 6ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * under the terms of the GNU General Public License version 2 only, as 7ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * published by the Free Software Foundation. Oracle designates this 8ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * particular file as subject to the "Classpath" exception as provided 9ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * by Oracle in the LICENSE file that accompanied this code. 10ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 11ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * This code is distributed in the hope that it will be useful, but WITHOUT 12ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * version 2 for more details (a copy is included in the LICENSE file that 15ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * accompanied this code). 16ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 17ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * You should have received a copy of the GNU General Public License version 18ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 2 along with this work; if not, write to the Free Software Foundation, 19ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 21ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or visit www.oracle.com if you need additional information or have any 23ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * questions. 24ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 25ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinpackage java.util.stream; 26ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 27ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.nio.charset.Charset; 28ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Arrays; 29ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Collection; 30ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Comparator; 31ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Iterator; 32ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Objects; 33ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Optional; 34ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Spliterator; 35ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.Spliterators; 36ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.concurrent.ConcurrentHashMap; 37ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.BiConsumer; 38ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.BiFunction; 39ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.BinaryOperator; 40ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.Consumer; 41ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.Function; 42ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.IntFunction; 43ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.Predicate; 44ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.Supplier; 45ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.ToDoubleFunction; 46ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.ToIntFunction; 47ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.ToLongFunction; 48ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinimport java.util.function.UnaryOperator; 49ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 50ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin/** 51ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * A sequence of elements supporting sequential and parallel aggregate 52ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operations. The following example illustrates an aggregate operation using 53ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link Stream} and {@link IntStream}: 54ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 55ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 56ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * int sum = widgets.stream() 57ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .filter(w -> w.getColor() == RED) 58ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .mapToInt(w -> w.getWeight()) 59ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .sum(); 60ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 61ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 62ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * In this example, {@code widgets} is a {@code Collection<Widget>}. We create 63ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * a stream of {@code Widget} objects via {@link Collection#stream Collection.stream()}, 64ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * filter it to produce a stream containing only the red widgets, and then 65ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * transform it into a stream of {@code int} values representing the weight of 66ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * each red widget. Then this stream is summed to produce a total weight. 67ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 68ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>In addition to {@code Stream}, which is a stream of object references, 69ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * there are primitive specializations for {@link IntStream}, {@link LongStream}, 70ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * and {@link DoubleStream}, all of which are referred to as "streams" and 71ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * conform to the characteristics and restrictions described here. 72ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 73ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>To perform a computation, stream 74ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#StreamOps">operations</a> are composed into a 75ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <em>stream pipeline</em>. A stream pipeline consists of a source (which 76ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * might be an array, a collection, a generator function, an I/O channel, 77ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * etc), zero or more <em>intermediate operations</em> (which transform a 78ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream into another stream, such as {@link Stream#filter(Predicate)}), and a 79ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <em>terminal operation</em> (which produces a result or side-effect, such 80ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * as {@link Stream#count()} or {@link Stream#forEach(Consumer)}). 81ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Streams are lazy; computation on the source data is only performed when the 82ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * terminal operation is initiated, and source elements are consumed only 83ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * as needed. 84ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 85ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>Collections and streams, while bearing some superficial similarities, 86ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * have different goals. Collections are primarily concerned with the efficient 87ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * management of, and access to, their elements. By contrast, streams do not 88ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * provide a means to directly access or manipulate their elements, and are 89ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * instead concerned with declaratively describing their source and the 90ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * computational operations which will be performed in aggregate on that source. 91ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * However, if the provided stream operations do not offer the desired 92ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * functionality, the {@link #iterator()} and {@link #spliterator()} operations 93ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * can be used to perform a controlled traversal. 94ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 95ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>A stream pipeline, like the "widgets" example above, can be viewed as 96ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * a <em>query</em> on the stream source. Unless the source was explicitly 97ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * designed for concurrent modification (such as a {@link ConcurrentHashMap}), 98ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * unpredictable or erroneous behavior may result from modifying the stream 99ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * source while it is being queried. 100ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 101ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>Most stream operations accept parameters that describe user-specified 102ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * behavior, such as the lambda expression {@code w -> w.getWeight()} passed to 103ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code mapToInt} in the example above. To preserve correct behavior, 104ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * these <em>behavioral parameters</em>: 105ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <ul> 106ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <li>must be <a href="package-summary.html#NonInterference">non-interfering</a> 107ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * (they do not modify the stream source); and</li> 108ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <li>in most cases must be <a href="package-summary.html#Statelessness">stateless</a> 109ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * (their result should not depend on any state that might change during execution 110ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * of the stream pipeline).</li> 111ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * </ul> 112ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 113ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>Such parameters are always instances of a 114ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="../function/package-summary.html">functional interface</a> such 115ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * as {@link java.util.function.Function}, and are often lambda expressions or 116ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * method references. Unless otherwise specified these parameters must be 117ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <em>non-null</em>. 118ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 119ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>A stream should be operated on (invoking an intermediate or terminal stream 120ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation) only once. This rules out, for example, "forked" streams, where 121ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the same source feeds two or more pipelines, or multiple traversals of the 122ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * same stream. A stream implementation may throw {@link IllegalStateException} 123ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * if it detects that the stream is being reused. However, since some stream 124ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operations may return their receiver rather than a new stream object, it may 125ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * not be possible to detect reuse in all cases. 126ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 127ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>Streams have a {@link #close()} method and implement {@link AutoCloseable}, 128ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * but nearly all stream instances do not actually need to be closed after use. 129ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Generally, only streams whose source is an IO channel will require closing. Most streams 130ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * are backed by collections, arrays, or generating functions, which require no 131ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * special resource management. (If a stream does require closing, it can be 132ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * declared as a resource in a {@code try}-with-resources statement.) 133ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 134ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>Stream pipelines may execute either sequentially or in 135ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Parallelism">parallel</a>. This 136ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * execution mode is a property of the stream. Streams are created 137ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * with an initial choice of sequential or parallel execution. (For example, 138ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link Collection#stream() Collection.stream()} creates a sequential stream, 139ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * and {@link Collection#parallelStream() Collection.parallelStream()} creates 140ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * a parallel one.) This choice of execution mode may be modified by the 141ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link #sequential()} or {@link #parallel()} methods, and may be queried with 142ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the {@link #isParallel()} method. 143ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 144ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of the stream elements 145ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @since 1.8 146ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see IntStream 147ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see LongStream 148ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see DoubleStream 149ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see <a href="package-summary.html">java.util.stream</a> 150ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 151ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkinpublic interface Stream<T> extends BaseStream<T, Stream<T>> { 152ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 153ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 154ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the elements of this stream that match 155ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the given predicate. 156ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 157ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 158ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 159ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 160ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, 161ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 162ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate to apply to each element to determine if it 163ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * should be included 164ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 165ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 166ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> filter(Predicate<? super T> predicate); 167ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 168ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 169ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the results of applying the given 170ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to the elements of this stream. 171ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 172ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 173ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 174ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 175ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <R> The element type of the new stream 176ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 177ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 178ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element 179ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 180ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 181ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin <R> Stream<R> map(Function<? super T, ? extends R> mapper); 182ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 183ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 184ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an {@code IntStream} consisting of the results of applying the 185ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * given function to the elements of this stream. 186ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 187ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps"> 188ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * intermediate operation</a>. 189ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 190ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 191ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 192ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element 193ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 194ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 195ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin IntStream mapToInt(ToIntFunction<? super T> mapper); 196ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 197ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 198ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a {@code LongStream} consisting of the results of applying the 199ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * given function to the elements of this stream. 200ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 201ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 202ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 203ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 204ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 205ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 206ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element 207ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 208ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 209ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin LongStream mapToLong(ToLongFunction<? super T> mapper); 210ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 211ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 212ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a {@code DoubleStream} consisting of the results of applying the 213ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * given function to the elements of this stream. 214ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 215ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 216ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 217ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 218ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 219ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 220ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element 221ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 222ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 223ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin DoubleStream mapToDouble(ToDoubleFunction<? super T> mapper); 224ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 225ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 226ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the results of replacing each element of 227ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * this stream with the contents of a mapped stream produced by applying 228ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the provided mapping function to each element. Each mapped stream is 229ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link java.util.stream.BaseStream#close() closed} after its contents 230ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * have been placed into this stream. (If a mapped stream is {@code null} 231ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * an empty stream is used, instead.) 232ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 233ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 234ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 235ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 236ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 237ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The {@code flatMap()} operation has the effect of applying a one-to-many 238ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * transformation to the elements of the stream, and then flattening the 239ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * resulting elements into a new stream. 240ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 241ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p><b>Examples.</b> 242ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 243ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>If {@code orders} is a stream of purchase orders, and each purchase 244ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * order contains a collection of line items, then the following produces a 245ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream containing all the line items in all the orders: 246ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 247ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * orders.flatMap(order -> order.getLineItems().stream())... 248ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 249ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 250ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>If {@code path} is the path to a file, then the following produces a 251ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream of the {@code words} contained in that file: 252ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 253ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Stream<String> lines = Files.lines(path, StandardCharsets.UTF_8); 254ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Stream<String> words = lines.flatMap(line -> Stream.of(line.split(" +"))); 255ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 256ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The {@code mapper} function passed to {@code flatMap} splits a line, 257ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * using a simple regular expression, into an array of words, and then 258ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * creates a stream of words from that array. 259ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 260ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <R> The element type of the new stream 261ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 262ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 263ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element which produces a stream 264ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * of new values 265ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 266ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 267ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin <R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper); 268ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 269ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 270ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an {@code IntStream} consisting of the results of replacing each 271ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * element of this stream with the contents of a mapped stream produced by 272ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * applying the provided mapping function to each element. Each mapped 273ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream is {@link java.util.stream.BaseStream#close() closed} after its 274ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * contents have been placed into this stream. (If a mapped stream is 275ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code null} an empty stream is used, instead.) 276ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 277ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 278ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 279ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 280ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 281ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 282ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element which produces a stream 283ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * of new values 284ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 285ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #flatMap(Function) 286ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 287ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin IntStream flatMapToInt(Function<? super T, ? extends IntStream> mapper); 288ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 289ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 290ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an {@code LongStream} consisting of the results of replacing each 291ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * element of this stream with the contents of a mapped stream produced by 292ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * applying the provided mapping function to each element. Each mapped 293ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream is {@link java.util.stream.BaseStream#close() closed} after its 294ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * contents have been placed into this stream. (If a mapped stream is 295ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code null} an empty stream is used, instead.) 296ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 297ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 298ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 299ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 300ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 301ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 302ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element which produces a stream 303ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * of new values 304ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 305ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #flatMap(Function) 306ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 307ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin LongStream flatMapToLong(Function<? super T, ? extends LongStream> mapper); 308ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 309ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 310ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an {@code DoubleStream} consisting of the results of replacing 311ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * each element of this stream with the contents of a mapped stream produced 312ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * by applying the provided mapping function to each element. Each mapped 313ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream is {@link java.util.stream.BaseStream#close() closed} after its 314ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * contents have placed been into this stream. (If a mapped stream is 315ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code null} an empty stream is used, instead.) 316ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 317ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 318ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 319ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 320ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, 321ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 322ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function to apply to each element which produces a stream 323ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * of new values 324ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 325ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #flatMap(Function) 326ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 327ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin DoubleStream flatMapToDouble(Function<? super T, ? extends DoubleStream> mapper); 328ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 329ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 330ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the distinct elements (according to 331ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link Object#equals(Object)}) of this stream. 332ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 333ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>For ordered streams, the selection of distinct elements is stable 334ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * (for duplicated elements, the element appearing first in the encounter 335ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * order is preserved.) For unordered streams, no stability guarantees 336ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * are made. 337ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 338ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">stateful 339ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * intermediate operation</a>. 340ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 341ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 342ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Preserving stability for {@code distinct()} in parallel pipelines is 343ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * relatively expensive (requires that the operation act as a full barrier, 344ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * with substantial buffering overhead), and stability is often not needed. 345ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Using an unordered stream source (such as {@link #generate(Supplier)}) 346ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or removing the ordering constraint with {@link #unordered()} may result 347ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * in significantly more efficient execution for {@code distinct()} in parallel 348ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * pipelines, if the semantics of your situation permit. If consistency 349ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * with encounter order is required, and you are experiencing poor performance 350ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or memory utilization with {@code distinct()} in parallel pipelines, 351ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * switching to sequential execution with {@link #sequential()} may improve 352ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * performance. 353ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 354ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 355ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 356ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> distinct(); 357ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 358ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 359ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the elements of this stream, sorted 360ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * according to natural order. If the elements of this stream are not 361ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Comparable}, a {@code java.lang.ClassCastException} may be thrown 362ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * when the terminal operation is executed. 363ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 364ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>For ordered streams, the sort is stable. For unordered streams, no 365ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stability guarantees are made. 366ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 367ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">stateful 368ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * intermediate operation</a>. 369ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 370ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 371ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 372ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> sorted(); 373ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 374ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 375ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the elements of this stream, sorted 376ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * according to the provided {@code Comparator}. 377ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 378ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>For ordered streams, the sort is stable. For unordered streams, no 379ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stability guarantees are made. 380ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 381ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">stateful 382ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * intermediate operation</a>. 383ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 384ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param comparator a <a href="package-summary.html#NonInterference">non-interfering</a>, 385ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 386ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Comparator} to be used to compare stream elements 387ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 388ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 389ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> sorted(Comparator<? super T> comparator); 390ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 391ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 392ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the elements of this stream, additionally 393ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * performing the provided action on each element as elements are consumed 394ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * from the resulting stream. 395ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 396ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is an <a href="package-summary.html#StreamOps">intermediate 397ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 398ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 399ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>For parallel stream pipelines, the action may be called at 400ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * whatever time and in whatever thread the element is made available by the 401ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * upstream operation. If the action modifies shared state, 402ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * it is responsible for providing the required synchronization. 403ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 404ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote This method exists mainly to support debugging, where you want 405ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * to see the elements as they flow past a certain point in a pipeline: 406ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 407ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Stream.of("one", "two", "three", "four") 408ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .filter(e -> e.length() > 3) 409ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .peek(e -> System.out.println("Filtered value: " + e)) 410ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .map(String::toUpperCase) 411ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .peek(e -> System.out.println("Mapped value: " + e)) 412ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .collect(Collectors.toList()); 413ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 414ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 415ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param action a <a href="package-summary.html#NonInterference"> 416ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * non-interfering</a> action to perform on the elements as 417ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * they are consumed from the stream 418ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 419ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 420ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> peek(Consumer<? super T> action); 421ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 422ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 423ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the elements of this stream, truncated 424ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * to be no longer than {@code maxSize} in length. 425ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 426ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 427ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stateful intermediate operation</a>. 428ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 429ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 430ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * While {@code limit()} is generally a cheap operation on sequential 431ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream pipelines, it can be quite expensive on ordered parallel pipelines, 432ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * especially for large values of {@code maxSize}, since {@code limit(n)} 433ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * is constrained to return not just any <em>n</em> elements, but the 434ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <em>first n</em> elements in the encounter order. Using an unordered 435ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream source (such as {@link #generate(Supplier)}) or removing the 436ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * ordering constraint with {@link #unordered()} may result in significant 437ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * speedups of {@code limit()} in parallel pipelines, if the semantics of 438ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * your situation permit. If consistency with encounter order is required, 439ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * and you are experiencing poor performance or memory utilization with 440ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code limit()} in parallel pipelines, switching to sequential execution 441ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * with {@link #sequential()} may improve performance. 442ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 443ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param maxSize the number of elements the stream should be limited to 444ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 445ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws IllegalArgumentException if {@code maxSize} is negative 446ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 447ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> limit(long maxSize); 448ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 449ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 450ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a stream consisting of the remaining elements of this stream 451ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * after discarding the first {@code n} elements of the stream. 452ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * If this stream contains fewer than {@code n} elements then an 453ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * empty stream will be returned. 454ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 455ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">stateful 456ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * intermediate operation</a>. 457ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 458ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 459ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * While {@code skip()} is generally a cheap operation on sequential 460ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream pipelines, it can be quite expensive on ordered parallel pipelines, 461ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * especially for large values of {@code n}, since {@code skip(n)} 462ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * is constrained to skip not just any <em>n</em> elements, but the 463ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <em>first n</em> elements in the encounter order. Using an unordered 464ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream source (such as {@link #generate(Supplier)}) or removing the 465ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * ordering constraint with {@link #unordered()} may result in significant 466ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * speedups of {@code skip()} in parallel pipelines, if the semantics of 467ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * your situation permit. If consistency with encounter order is required, 468ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * and you are experiencing poor performance or memory utilization with 469ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code skip()} in parallel pipelines, switching to sequential execution 470ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * with {@link #sequential()} may improve performance. 471ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 472ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param n the number of leading elements to skip 473ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 474ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws IllegalArgumentException if {@code n} is negative 475ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 476ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> skip(long n); 477ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 478ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 479ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs an action for each element of this stream. 480ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 481ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 482ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 483ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 484ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The behavior of this operation is explicitly nondeterministic. 485ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * For parallel stream pipelines, this operation does <em>not</em> 486ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * guarantee to respect the encounter order of the stream, as doing so 487ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * would sacrifice the benefit of parallelism. For any given element, the 488ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * action may be performed at whatever time and in whatever thread the 489ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * library chooses. If the action accesses shared state, it is 490ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * responsible for providing the required synchronization. 491ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 492ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param action a <a href="package-summary.html#NonInterference"> 493ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * non-interfering</a> action to perform on the elements 494ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 495ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin void forEach(Consumer<? super T> action); 496ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 497ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 498ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs an action for each element of this stream, in the encounter 499ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * order of the stream if the stream has a defined encounter order. 500ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 501ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 502ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 503ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 504ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This operation processes the elements one at a time, in encounter 505ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * order if one exists. Performing the action for one element 506ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a> 507ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * performing the action for subsequent elements, but for any given element, 508ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the action may be performed in whatever thread the library chooses. 509ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 510ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param action a <a href="package-summary.html#NonInterference"> 511ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * non-interfering</a> action to perform on the elements 512ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #forEach(Consumer) 513ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 514ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin void forEachOrdered(Consumer<? super T> action); 515ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 516ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 517ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an array containing the elements of this stream. 518ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 519ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 520ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 521ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 522ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an array containing the elements of this stream 523ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 524ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Object[] toArray(); 525ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 526ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 527ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an array containing the elements of this stream, using the 528ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * provided {@code generator} function to allocate the returned array, as 529ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * well as any additional arrays that might be required for a partitioned 530ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * execution or for resizing. 531ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 532ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 533ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 534ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 535ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 536ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The generator function takes an integer, which is the size of the 537ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * desired array, and produces an array of the desired size. This can be 538ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * concisely expressed with an array constructor reference: 539ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 540ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Person[] men = people.stream() 541ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .filter(p -> p.getGender() == MALE) 542ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .toArray(Person[]::new); 543ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 544ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 545ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <A> the element type of the resulting array 546ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param generator a function which produces a new array of the desired 547ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * type and the provided length 548ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an array containing the elements in this stream 549ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws ArrayStoreException if the runtime type of the array returned 550ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * from the array generator is not a supertype of the runtime type of every 551ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * element in this stream 552ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 553ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin <A> A[] toArray(IntFunction<A[]> generator); 554ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 555ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 556ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs a <a href="package-summary.html#Reduction">reduction</a> on the 557ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * elements of this stream, using the provided identity value and an 558ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Associativity">associative</a> 559ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * accumulation function, and returns the reduced value. This is equivalent 560ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * to: 561ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 562ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * T result = identity; 563ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * for (T element : this stream) 564ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * result = accumulator.apply(result, element) 565ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * return result; 566ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 567ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 568ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * but is not constrained to execute sequentially. 569ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 570ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The {@code identity} value must be an identity for the accumulator 571ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function. This means that for all {@code t}, 572ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code accumulator.apply(identity, t)} is equal to {@code t}. 573ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The {@code accumulator} function must be an 574ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Associativity">associative</a> function. 575ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 576ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 577ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 578ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 579ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote Sum, min, max, average, and string concatenation are all special 580ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * cases of reduction. Summing a stream of numbers can be expressed as: 581ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 582ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 583ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Integer sum = integers.reduce(0, (a, b) -> a+b); 584ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 585ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 586ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or: 587ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 588ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 589ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Integer sum = integers.reduce(0, Integer::sum); 590ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 591ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 592ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>While this may seem a more roundabout way to perform an aggregation 593ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * compared to simply mutating a running total in a loop, reduction 594ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operations parallelize more gracefully, without needing additional 595ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * synchronization and with greatly reduced risk of data races. 596ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 597ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param identity the identity value for the accumulating function 598ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param accumulator an <a href="package-summary.html#Associativity">associative</a>, 599ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#NonInterference">non-interfering</a>, 600ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 601ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function for combining two values 602ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the result of the reduction 603ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 604ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin T reduce(T identity, BinaryOperator<T> accumulator); 605ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 606ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 607ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs a <a href="package-summary.html#Reduction">reduction</a> on the 608ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * elements of this stream, using an 609ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Associativity">associative</a> accumulation 610ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function, and returns an {@code Optional} describing the reduced value, 611ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * if any. This is equivalent to: 612ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 613ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * boolean foundAny = false; 614ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * T result = null; 615ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * for (T element : this stream) { 616ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * if (!foundAny) { 617ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * foundAny = true; 618ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * result = element; 619ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * } 620ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * else 621ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * result = accumulator.apply(result, element); 622ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * } 623ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * return foundAny ? Optional.of(result) : Optional.empty(); 624ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 625ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 626ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * but is not constrained to execute sequentially. 627ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 628ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The {@code accumulator} function must be an 629ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Associativity">associative</a> function. 630ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 631ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 632ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 633ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 634ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param accumulator an <a href="package-summary.html#Associativity">associative</a>, 635ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#NonInterference">non-interfering</a>, 636ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 637ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function for combining two values 638ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an {@link Optional} describing the result of the reduction 639ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws NullPointerException if the result of the reduction is null 640ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #reduce(Object, BinaryOperator) 641ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #min(Comparator) 642ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #max(Comparator) 643ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 644ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Optional<T> reduce(BinaryOperator<T> accumulator); 645ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 646ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 647ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs a <a href="package-summary.html#Reduction">reduction</a> on the 648ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * elements of this stream, using the provided identity, accumulation and 649ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * combining functions. This is equivalent to: 650ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 651ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * U result = identity; 652ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * for (T element : this stream) 653ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * result = accumulator.apply(result, element) 654ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * return result; 655ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 656ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 657ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * but is not constrained to execute sequentially. 658ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 659ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The {@code identity} value must be an identity for the combiner 660ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function. This means that for all {@code u}, {@code combiner(identity, u)} 661ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * is equal to {@code u}. Additionally, the {@code combiner} function 662ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * must be compatible with the {@code accumulator} function; for all 663ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code u} and {@code t}, the following must hold: 664ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 665ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * combiner.apply(u, accumulator.apply(identity, t)) == accumulator.apply(u, t) 666ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 667ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 668ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 669ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 670ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 671ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote Many reductions using this form can be represented more simply 672ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * by an explicit combination of {@code map} and {@code reduce} operations. 673ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The {@code accumulator} function acts as a fused mapper and accumulator, 674ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * which can sometimes be more efficient than separate mapping and reduction, 675ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * such as when knowing the previously reduced value allows you to avoid 676ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * some computation. 677ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 678ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <U> The type of the result 679ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param identity the identity value for the combiner function 680ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param accumulator an <a href="package-summary.html#Associativity">associative</a>, 681ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#NonInterference">non-interfering</a>, 682ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 683ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function for incorporating an additional element into a result 684ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param combiner an <a href="package-summary.html#Associativity">associative</a>, 685ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#NonInterference">non-interfering</a>, 686ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 687ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function for combining two values, which must be 688ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * compatible with the accumulator function 689ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the result of the reduction 690ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #reduce(BinaryOperator) 691ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #reduce(Object, BinaryOperator) 692ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 693ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin <U> U reduce(U identity, 694ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin BiFunction<U, ? super T, U> accumulator, 695ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin BinaryOperator<U> combiner); 696ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 697ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 698ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs a <a href="package-summary.html#MutableReduction">mutable 699ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * reduction</a> operation on the elements of this stream. A mutable 700ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * reduction is one in which the reduced value is a mutable result container, 701ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * such as an {@code ArrayList}, and elements are incorporated by updating 702ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the state of the result rather than by replacing the result. This 703ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * produces a result equivalent to: 704ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 705ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * R result = supplier.get(); 706ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * for (T element : this stream) 707ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * accumulator.accept(result, element); 708ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * return result; 709ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 710ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 711ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations 712ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * can be parallelized without requiring additional synchronization. 713ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 714ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 715ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 716ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 717ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote There are many existing classes in the JDK whose signatures are 718ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * well-suited for use with method references as arguments to {@code collect()}. 719ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * For example, the following will accumulate strings into an {@code ArrayList}: 720ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 721ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add, 722ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * ArrayList::addAll); 723ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 724ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 725ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The following will take a stream of strings and concatenates them into a 726ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * single string: 727ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 728ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * String concat = stringStream.collect(StringBuilder::new, StringBuilder::append, 729ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * StringBuilder::append) 730ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * .toString(); 731ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 732ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 733ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <R> type of the result 734ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param supplier a function that creates a new result container. For a 735ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * parallel execution, this function may be called 736ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * multiple times and must return a fresh value each time. 737ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param accumulator an <a href="package-summary.html#Associativity">associative</a>, 738ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#NonInterference">non-interfering</a>, 739ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 740ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function for incorporating an additional element into a result 741ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param combiner an <a href="package-summary.html#Associativity">associative</a>, 742ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#NonInterference">non-interfering</a>, 743ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 744ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * function for combining two values, which must be 745ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * compatible with the accumulator function 746ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the result of the reduction 747ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 748ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin <R> R collect(Supplier<R> supplier, 749ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin BiConsumer<R, ? super T> accumulator, 750ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin BiConsumer<R, R> combiner); 751ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 752ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 753ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Performs a <a href="package-summary.html#MutableReduction">mutable 754ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * reduction</a> operation on the elements of this stream using a 755ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Collector}. A {@code Collector} 756ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * encapsulates the functions used as arguments to 757ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link #collect(Supplier, BiConsumer, BiConsumer)}, allowing for reuse of 758ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * collection strategies and composition of collect operations such as 759ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * multiple-level grouping or partitioning. 760ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 761ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>If the stream is parallel, and the {@code Collector} 762ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * is {@link Collector.Characteristics#CONCURRENT concurrent}, and 763ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * either the stream is unordered or the collector is 764ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@link Collector.Characteristics#UNORDERED unordered}, 765ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * then a concurrent reduction will be performed (see {@link Collector} for 766ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * details on concurrent reduction.) 767ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 768ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 769ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 770ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 771ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>When executed in parallel, multiple intermediate results may be 772ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * instantiated, populated, and merged so as to maintain isolation of 773ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * mutable data structures. Therefore, even when executed in parallel 774ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * with non-thread-safe data structures (such as {@code ArrayList}), no 775ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * additional synchronization is needed for a parallel reduction. 776ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 777ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 778ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The following will accumulate strings into an ArrayList: 779ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 780ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * List<String> asList = stringStream.collect(Collectors.toList()); 781ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 782ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 783ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The following will classify {@code Person} objects by city: 784ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 785ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Map<String, List<Person>> peopleByCity 786ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * = personStream.collect(Collectors.groupingBy(Person::getCity)); 787ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 788ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 789ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The following will classify {@code Person} objects by state and city, 790ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * cascading two {@code Collector}s together: 791ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 792ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Map<String, Map<String, List<Person>>> peopleByStateAndCity 793ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * = personStream.collect(Collectors.groupingBy(Person::getState, 794ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Collectors.groupingBy(Person::getCity))); 795ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 796ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 797ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <R> the type of the result 798ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <A> the intermediate accumulation type of the {@code Collector} 799ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param collector the {@code Collector} describing the reduction 800ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the result of the reduction 801ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #collect(Supplier, BiConsumer, BiConsumer) 802ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see Collectors 803ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 804ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin <R, A> R collect(Collector<? super T, A, R> collector); 805ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 806ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 807ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns the minimum element of this stream according to the provided 808ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Comparator}. This is a special case of a 809ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Reduction">reduction</a>. 810ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 811ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>. 812ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 813ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param comparator a <a href="package-summary.html#NonInterference">non-interfering</a>, 814ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 815ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Comparator} to compare elements of this stream 816ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an {@code Optional} describing the minimum element of this stream, 817ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or an empty {@code Optional} if the stream is empty 818ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws NullPointerException if the minimum element is null 819ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 820ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Optional<T> min(Comparator<? super T> comparator); 821ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 822ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 823ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns the maximum element of this stream according to the provided 824ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Comparator}. This is a special case of a 825ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Reduction">reduction</a>. 826ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 827ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal 828ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * operation</a>. 829ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 830ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param comparator a <a href="package-summary.html#NonInterference">non-interfering</a>, 831ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 832ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Comparator} to compare elements of this stream 833ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an {@code Optional} describing the maximum element of this stream, 834ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or an empty {@code Optional} if the stream is empty 835ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws NullPointerException if the maximum element is null 836ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 837ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Optional<T> max(Comparator<? super T> comparator); 838ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 839ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 840ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns the count of elements in this stream. This is a special case of 841ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * a <a href="package-summary.html#Reduction">reduction</a> and is 842ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * equivalent to: 843ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 844ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * return mapToLong(e -> 1L).sum(); 845ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 846ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 847ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>. 848ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 849ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the count of elements in this stream 850ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 851ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin long count(); 852ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 853ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 854ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns whether any elements of this stream match the provided 855ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate. May not evaluate the predicate on all elements if not 856ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * necessary for determining the result. If the stream is empty then 857ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code false} is returned and the predicate is not evaluated. 858ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 859ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 860ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * terminal operation</a>. 861ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 862ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 863ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * This method evaluates the <em>existential quantification</em> of the 864ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate over the elements of the stream (for some x P(x)). 865ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 866ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, 867ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 868ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate to apply to elements of this stream 869ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return {@code true} if any elements of the stream match the provided 870ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate, otherwise {@code false} 871ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 872ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin boolean anyMatch(Predicate<? super T> predicate); 873ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 874ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 875ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns whether all elements of this stream match the provided predicate. 876ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * May not evaluate the predicate on all elements if not necessary for 877ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * determining the result. If the stream is empty then {@code true} is 878ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * returned and the predicate is not evaluated. 879ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 880ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 881ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * terminal operation</a>. 882ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 883ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 884ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * This method evaluates the <em>universal quantification</em> of the 885ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate over the elements of the stream (for all x P(x)). If the 886ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * stream is empty, the quantification is said to be <em>vacuously 887ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * satisfied</em> and is always {@code true} (regardless of P(x)). 888ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 889ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, 890ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 891ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate to apply to elements of this stream 892ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return {@code true} if either all elements of the stream match the 893ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * provided predicate or the stream is empty, otherwise {@code false} 894ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 895ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin boolean allMatch(Predicate<? super T> predicate); 896ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 897ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 898ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns whether no elements of this stream match the provided predicate. 899ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * May not evaluate the predicate on all elements if not necessary for 900ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * determining the result. If the stream is empty then {@code true} is 901ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * returned and the predicate is not evaluated. 902ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 903ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 904ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * terminal operation</a>. 905ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 906ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @apiNote 907ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * This method evaluates the <em>universal quantification</em> of the 908ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * negated predicate over the elements of the stream (for all x ~P(x)). If 909ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the stream is empty, the quantification is said to be vacuously satisfied 910ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * and is always {@code true}, regardless of P(x). 911ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 912ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, 913ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <a href="package-summary.html#Statelessness">stateless</a> 914ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * predicate to apply to elements of this stream 915ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return {@code true} if either no elements of the stream match the 916ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * provided predicate or the stream is empty, otherwise {@code false} 917ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 918ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin boolean noneMatch(Predicate<? super T> predicate); 919ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 920ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 921ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an {@link Optional} describing the first element of this stream, 922ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or an empty {@code Optional} if the stream is empty. If the stream has 923ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * no encounter order, then any element may be returned. 924ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 925ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 926ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * terminal operation</a>. 927ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 928ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an {@code Optional} describing the first element of this stream, 929ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * or an empty {@code Optional} if the stream is empty 930ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws NullPointerException if the element selected is null 931ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 932ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Optional<T> findFirst(); 933ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 934ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 935ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an {@link Optional} describing some element of the stream, or an 936ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * empty {@code Optional} if the stream is empty. 937ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 938ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 939ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * terminal operation</a>. 940ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 941ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The behavior of this operation is explicitly nondeterministic; it is 942ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * free to select any element in the stream. This is to allow for maximal 943ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * performance in parallel operations; the cost is that multiple invocations 944ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * on the same source may not return the same result. (If a stable result 945ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * is desired, use {@link #findFirst()} instead.) 946ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 947ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an {@code Optional} describing some element of this stream, or an 948ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * empty {@code Optional} if the stream is empty 949ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws NullPointerException if the element selected is null 950ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see #findFirst() 951ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 952ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Optional<T> findAny(); 953ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 954ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin // Static factories 955ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 956ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 957ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a builder for a {@code Stream}. 958ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 959ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> type of elements 960ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return a stream builder 961ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 962ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static<T> Builder<T> builder() { 963ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return new Streams.StreamBuilderImpl<>(); 964ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 965ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 966ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 967ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an empty sequential {@code Stream}. 968ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 969ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of stream elements 970ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return an empty sequential stream 971ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 972ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static<T> Stream<T> empty() { 973ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return StreamSupport.stream(Spliterators.<T>emptySpliterator(), false); 974ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 975ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 976ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 977ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a sequential {@code Stream} containing a single element. 978ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 979ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param t the single element 980ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of stream elements 981ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return a singleton sequential stream 982ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 983ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static<T> Stream<T> of(T t) { 984ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false); 985ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 986ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 987ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 988ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns a sequential ordered stream whose elements are the specified values. 989ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 990ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of stream elements 991ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param values the elements of the new stream 992ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the new stream 993ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 994ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @SafeVarargs 995ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @SuppressWarnings("varargs") // Creating a stream from an array is safe 996ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static<T> Stream<T> of(T... values) { 997ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return Arrays.stream(values); 998ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 999ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1000ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1001ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an infinite sequential ordered {@code Stream} produced by iterative 1002ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * application of a function {@code f} to an initial element {@code seed}, 1003ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * producing a {@code Stream} consisting of {@code seed}, {@code f(seed)}, 1004ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code f(f(seed))}, etc. 1005ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1006ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>The first element (position {@code 0}) in the {@code Stream} will be 1007ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the provided {@code seed}. For {@code n > 0}, the element at position 1008ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code n}, will be the result of applying the function {@code f} to the 1009ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * element at position {@code n - 1}. 1010ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1011ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of stream elements 1012ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param seed the initial element 1013ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param f a function to be applied to to the previous element to produce 1014ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * a new element 1015ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return a new sequential {@code Stream} 1016ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1017ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static<T> Stream<T> iterate(final T seed, final UnaryOperator<T> f) { 1018ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Objects.requireNonNull(f); 1019ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin final Iterator<T> iterator = new Iterator<T>() { 1020ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @SuppressWarnings("unchecked") 1021ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin T t = (T) Streams.NONE; 1022ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1023ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @Override 1024ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public boolean hasNext() { 1025ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return true; 1026ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1027ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1028ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @Override 1029ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public T next() { 1030ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return t = (t == Streams.NONE) ? seed : f.apply(t); 1031ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1032ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin }; 1033ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return StreamSupport.stream(Spliterators.spliteratorUnknownSize( 1034ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin iterator, 1035ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Spliterator.ORDERED | Spliterator.IMMUTABLE), false); 1036ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1037ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1038ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1039ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Returns an infinite sequential unordered stream where each element is 1040ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * generated by the provided {@code Supplier}. This is suitable for 1041ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * generating constant streams, streams of random elements, etc. 1042ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1043ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of stream elements 1044ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param s the {@code Supplier} of generated elements 1045ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return a new infinite sequential unordered {@code Stream} 1046ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1047ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static<T> Stream<T> generate(Supplier<T> s) { 1048ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Objects.requireNonNull(s); 1049ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return StreamSupport.stream( 1050ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin new StreamSpliterators.InfiniteSupplyingSpliterator.OfRef<>(Long.MAX_VALUE, s), false); 1051ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1052ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1053ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1054ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Creates a lazily concatenated stream whose elements are all the 1055ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * elements of the first stream followed by all the elements of the 1056ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * second stream. The resulting stream is ordered if both 1057ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * of the input streams are ordered, and parallel if either of the input 1058ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * streams is parallel. When the resulting stream is closed, the close 1059ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * handlers for both input streams are invoked. 1060ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1061ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @implNote 1062ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Use caution when constructing streams from repeated concatenation. 1063ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Accessing an element of a deeply concatenated stream can result in deep 1064ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * call chains, or even {@code StackOverflowException}. 1065ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1066ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> The type of stream elements 1067ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param a the first stream 1068ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param b the second stream 1069ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the concatenation of the two input streams 1070ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1071ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b) { 1072ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Objects.requireNonNull(a); 1073ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Objects.requireNonNull(b); 1074ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1075ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @SuppressWarnings("unchecked") 1076ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Spliterator<T> split = new Streams.ConcatSpliterator.OfRef<>( 1077ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin (Spliterator<T>) a.spliterator(), (Spliterator<T>) b.spliterator()); 1078ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> stream = StreamSupport.stream(split, a.isParallel() || b.isParallel()); 1079ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return stream.onClose(Streams.composedClose(a, b)); 1080ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1081ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1082ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1083ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * A mutable builder for a {@code Stream}. This allows the creation of a 1084ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Stream} by generating elements individually and adding them to the 1085ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Builder} (without the copying overhead that comes from using 1086ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * an {@code ArrayList} as a temporary buffer.) 1087ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1088ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <p>A stream builder has a lifecycle, which starts in a building 1089ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * phase, during which elements can be added, and then transitions to a built 1090ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * phase, after which elements may not be added. The built phase begins 1091ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * when the {@link #build()} method is called, which creates an ordered 1092ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * {@code Stream} whose elements are the elements that were added to the stream 1093ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * builder, in the order they were added. 1094ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1095ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param <T> the type of stream elements 1096ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @see Stream#builder() 1097ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @since 1.8 1098ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1099ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin public interface Builder<T> extends Consumer<T> { 1100ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1101ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1102ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Adds an element to the stream being built. 1103ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1104ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws IllegalStateException if the builder has already transitioned to 1105ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the built state 1106ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1107ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin @Override 1108ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin void accept(T t); 1109ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1110ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1111ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Adds an element to the stream being built. 1112ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1113ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @implSpec 1114ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * The default implementation behaves as if: 1115ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * <pre>{@code 1116ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * accept(t) 1117ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * return this; 1118ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * }</pre> 1119ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1120ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @param t the element to add 1121ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return {@code this} builder 1122ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws IllegalStateException if the builder has already transitioned to 1123ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the built state 1124ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1125ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin default Builder<T> add(T t) { 1126ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin accept(t); 1127ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin return this; 1128ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1129ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1130ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin /** 1131ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * Builds the stream, transitioning this builder to the built state. 1132ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * An {@code IllegalStateException} is thrown if there are further attempts 1133ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * to operate on the builder after it has entered the built state. 1134ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * 1135ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @return the built stream 1136ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * @throws IllegalStateException if the builder has already transitioned to 1137ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin * the built state 1138ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin */ 1139ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin Stream<T> build(); 1140ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin 1141ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin } 1142ff18b5f136f92154f2e05217e3953d10f459e561Igor Murashkin} 1143