Iterator.java revision 309f9df28350e15445b9135e8b710fa2b34b5dc1 
1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
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11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
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24 */
25
26package java.util;
27
28import java.util.function.Consumer;
29
30/**
31 * An iterator over a collection.  {@code Iterator} takes the place of
32 * {@link Enumeration} in the Java Collections Framework.  Iterators
33 * differ from enumerations in two ways:
34 *
35 * <ul>
36 *      <li> Iterators allow the caller to remove elements from the
37 *           underlying collection during the iteration with well-defined
38 *           semantics.
39 *      <li> Method names have been improved.
40 * </ul>
41 *
42 * <p>This interface is a member of the
43 * <a href="{@docRoot}openjdk-redirect.html?v=8&path=/technotes/guides/collections/index.html">
44 * Java Collections Framework</a>.
45 *
46 * @param <E> the type of elements returned by this iterator
47 *
48 * @author  Josh Bloch
49 * @see Collection
50 * @see ListIterator
51 * @see Iterable
52 * @since 1.2
53 */
54public interface Iterator<E> {
55    /**
56     * Returns {@code true} if the iteration has more elements.
57     * (In other words, returns {@code true} if {@link #next} would
58     * return an element rather than throwing an exception.)
59     *
60     * @return {@code true} if the iteration has more elements
61     */
62    boolean hasNext();
63
64    /**
65     * Returns the next element in the iteration.
66     *
67     * @return the next element in the iteration
68     * @throws NoSuchElementException if the iteration has no more elements
69     */
70    E next();
71
72    /**
73     * Removes from the underlying collection the last element returned
74     * by this iterator (optional operation).  This method can be called
75     * only once per call to {@link #next}.  The behavior of an iterator
76     * is unspecified if the underlying collection is modified while the
77     * iteration is in progress in any way other than by calling this
78     * method.
79     *
80     * @implSpec
81     * The default implementation throws an instance of
82     * {@link UnsupportedOperationException} and performs no other action.
83     *
84     * @throws UnsupportedOperationException if the {@code remove}
85     *         operation is not supported by this iterator
86     *
87     * @throws IllegalStateException if the {@code next} method has not
88     *         yet been called, or the {@code remove} method has already
89     *         been called after the last call to the {@code next}
90     *         method
91     */
92    default void remove() {
93        throw new UnsupportedOperationException("remove");
94    }
95
96    /**
97     * Performs the given action for each remaining element until all elements
98     * have been processed or the action throws an exception.  Actions are
99     * performed in the order of iteration, if that order is specified.
100     * Exceptions thrown by the action are relayed to the caller.
101     *
102     * @implSpec
103     * <p>The default implementation behaves as if:
104     * <pre>{@code
105     *     while (hasNext())
106     *         action.accept(next());
107     * }</pre>
108     *
109     * @param action The action to be performed for each element
110     * @throws NullPointerException if the specified action is null
111     * @since 1.8
112     */
113    default void forEachRemaining(Consumer<? super E> action) {
114        Objects.requireNonNull(action);
115        while (hasNext())
116            action.accept(next());
117    }
118}
119