OptionalInt.java revision b0576a2458c789126957917d8d9cf2a58ec6762a 
1/*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
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.
10 *
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).
16 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25package java.util;
26
27import java.util.function.IntConsumer;
28import java.util.function.IntSupplier;
29import java.util.function.Supplier;
30
31/**
32 * A container object which may or may not contain a {@code int} value.
33 * If a value is present, {@code isPresent()} will return {@code true} and
34 * {@code getAsInt()} will return the value.
35 *
36 * <p>Additional methods that depend on the presence or absence of a contained
37 * value are provided, such as {@link #orElse(int) orElse()}
38 * (return a default value if value not present) and
39 * {@link #ifPresent(java.util.function.IntConsumer) ifPresent()} (execute a block
40 * of code if the value is present).
41 *
42 * @since 1.8
43 */
44public final class OptionalInt {
45    /**
46     * Common instance for {@code empty()}.
47     */
48    private static final OptionalInt EMPTY = new OptionalInt();
49
50    /**
51     * If true then the value is present, otherwise indicates no value is present
52     */
53    private final boolean isPresent;
54    private final int value;
55
56    /**
57     * Construct an empty instance.
58     *
59     * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
60     * should exist per VM.
61     */
62    private OptionalInt() {
63        this.isPresent = false;
64        this.value = 0;
65    }
66
67    /**
68     * Returns an empty {@code OptionalInt} instance.  No value is present for this
69     * OptionalInt.
70     *
71     * @apiNote Though it may be tempting to do so, avoid testing if an object
72     * is empty by comparing with {@code ==} against instances returned by
73     * {@code Option.empty()}. There is no guarantee that it is a singleton.
74     * Instead, use {@link #isPresent()}.
75     *
76     *  @return an empty {@code OptionalInt}
77     */
78    public static OptionalInt empty() {
79        return EMPTY;
80    }
81
82    /**
83     * Construct an instance with the value present.
84     *
85     * @param value the int value to be present
86     */
87    private OptionalInt(int value) {
88        this.isPresent = true;
89
90        this.value = value;
91    }
92
93    /**
94     * Return an {@code OptionalInt} with the specified value present.
95     *
96     * @param value the value to be present
97     * @return an {@code OptionalInt} with the value present
98     */
99    public static OptionalInt of(int value) {
100        return new OptionalInt(value);
101    }
102
103    /**
104     * If a value is present in this {@code OptionalInt}, returns the value,
105     * otherwise throws {@code NoSuchElementException}.
106     *
107     * @return the value held by this {@code OptionalInt}
108     * @throws NoSuchElementException if there is no value present
109     *
110     * @see OptionalInt#isPresent()
111     */
112    public int getAsInt() {
113        if (!isPresent) {
114            throw new NoSuchElementException("No value present");
115        }
116        return value;
117    }
118
119    /**
120     * Return {@code true} if there is a value present, otherwise {@code false}.
121     *
122     * @return {@code true} if there is a value present, otherwise {@code false}
123     */
124    public boolean isPresent() {
125        return isPresent;
126    }
127
128    /**
129     * Have the specified consumer accept the value if a value is present,
130     * otherwise do nothing.
131     *
132     * @param consumer block to be executed if a value is present
133     * @throws NullPointerException if value is present and {@code consumer} is
134     * null
135     */
136    public void ifPresent(IntConsumer consumer) {
137        if (isPresent)
138            consumer.accept(value);
139    }
140
141    /**
142     * Return the value if present, otherwise return {@code other}.
143     *
144     * @param other the value to be returned if there is no value present
145     * @return the value, if present, otherwise {@code other}
146     */
147    public int orElse(int other) {
148        return isPresent ? value : other;
149    }
150
151    /**
152     * Return the value if present, otherwise invoke {@code other} and return
153     * the result of that invocation.
154     *
155     * @param other a {@code IntSupplier} whose result is returned if no value
156     * is present
157     * @return the value if present otherwise the result of {@code other.getAsInt()}
158     * @throws NullPointerException if value is not present and {@code other} is
159     * null
160     */
161    public int orElseGet(IntSupplier other) {
162        return isPresent ? value : other.getAsInt();
163    }
164
165    /**
166     * Return the contained value, if present, otherwise throw an exception
167     * to be created by the provided supplier.
168     *
169     * @apiNote A method reference to the exception constructor with an empty
170     * argument list can be used as the supplier. For example,
171     * {@code IllegalStateException::new}
172     *
173     * @param <X> Type of the exception to be thrown
174     * @param exceptionSupplier The supplier which will return the exception to
175     * be thrown
176     * @return the present value
177     * @throws X if there is no value present
178     * @throws NullPointerException if no value is present and
179     * {@code exceptionSupplier} is null
180     */
181    public<X extends Throwable> int orElseThrow(Supplier<X> exceptionSupplier) throws X {
182        if (isPresent) {
183            return value;
184        } else {
185            throw exceptionSupplier.get();
186        }
187    }
188
189    /**
190     * Indicates whether some other object is "equal to" this OptionalInt. The
191     * other object is considered equal if:
192     * <ul>
193     * <li>it is also an {@code OptionalInt} and;
194     * <li>both instances have no value present or;
195     * <li>the present values are "equal to" each other via {@code ==}.
196     * </ul>
197     *
198     * @param obj an object to be tested for equality
199     * @return {code true} if the other object is "equal to" this object
200     * otherwise {@code false}
201     */
202    @Override
203    public boolean equals(Object obj) {
204        if (this == obj) {
205            return true;
206        }
207
208        if (!(obj instanceof OptionalInt)) {
209            return false;
210        }
211
212        OptionalInt other = (OptionalInt) obj;
213        return (isPresent && other.isPresent)
214                ? value == other.value
215                : isPresent == other.isPresent;
216    }
217
218    /**
219     * Returns the hash code value of the present value, if any, or 0 (zero) if
220     * no value is present.
221     *
222     * @return hash code value of the present value or 0 if no value is present
223     */
224    @Override
225    public int hashCode() {
226        return isPresent ? Integer.hashCode(value) : 0;
227    }
228
229    /**
230     * {@inheritDoc}
231     *
232     * Returns a non-empty string representation of this object suitable for
233     * debugging. The exact presentation format is unspecified and may vary
234     * between implementations and versions.
235     *
236     * @implSpec If a value is present the result must include its string
237     * representation in the result. Empty and present instances must be
238     * unambiguously differentiable.
239     *
240     * @return the string representation of this instance
241     */
242    @Override
243    public String toString() {
244        return isPresent
245                ? String.format("OptionalInt[%s]", value)
246                : "OptionalInt.empty";
247    }
248}
249