1 /*
2 * Copyright (c) 2012, 2015, 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
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25 package java.util;
26
27 import java.util.function.IntConsumer;
28 import java.util.function.IntSupplier;
29 import java.util.function.Supplier;
30 import java.util.stream.IntStream;
31
32 /**
33 * A container object which may or may not contain an {@code int} value. If a
34 * value is present, {@code isPresent()} returns {@code true} and
35 * {@code getAsInt()} returns the value.
36 *
37 * <p>Additional methods that depend on the presence or absence of a contained
38 * value are provided, such as {@link #orElse(int) orElse()}
39 * (returns a default value if no value is present) and
40 * {@link #ifPresent(java.util.function.IntConsumer) ifPresent()} (performs an
41 * action if a value is present).
42 *
43 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
44 * class; use of identity-sensitive operations (including reference equality
45 * ({@code ==}), identity hash code, or synchronization) on instances of
46 * {@code OptionalInt} may have unpredictable results and should be avoided.
47 *
48 * @since 1.8
49 */
50 public final class OptionalInt {
51 /**
52 * Common instance for {@code empty()}.
53 */
54 private static final OptionalInt EMPTY = new OptionalInt();
55
56 /**
57 * If true then the value is present, otherwise indicates no value is present
58 */
59 private final boolean isPresent;
60 private final int value;
61
62 /**
63 * Construct an empty instance.
64 *
65 * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
66 * should exist per VM.
67 */
68 private OptionalInt() {
69 this.isPresent = false;
70 this.value = 0;
71 }
72
73 /**
74 * Returns an empty {@code OptionalInt} instance. No value is present for
75 * this {@code OptionalInt}.
76 *
77 * @apiNote
78 * Though it may be tempting to do so, avoid testing if an object is empty
79 * by comparing with {@code ==} against instances returned by
80 * {@code OptionalInt.empty()}. There is no guarantee that it is a singleton.
81 * Instead, use {@link #isPresent()}.
82 *
83 * @return an empty {@code OptionalInt}
84 */
85 public static OptionalInt empty() {
86 return EMPTY;
87 }
88
89 /**
90 * Construct an instance with the described value.
91 *
92 * @param value the int value to describe
93 */
94 private OptionalInt(int value) {
95 this.isPresent = true;
96 this.value = value;
97 }
98
99 /**
100 * Returns an {@code OptionalInt} describing the given value.
101 *
102 * @param value the value to describe
103 * @return an {@code OptionalInt} with the value present
104 */
105 public static OptionalInt of(int value) {
106 return new OptionalInt(value);
107 }
108
109 /**
110 * If a value is present, returns the value, otherwise throws
111 * {@code NoSuchElementException}.
112 *
113 * @return the value described by this {@code OptionalInt}
114 * @throws NoSuchElementException if no value is present
115 * @see OptionalInt#isPresent()
116 */
117 public int getAsInt() {
118 if (!isPresent) {
119 throw new NoSuchElementException("No value present");
120 }
121 return value;
122 }
123
124 /**
125 * If a value is present, returns {@code true}, otherwise {@code false}.
126 *
127 * @return {@code true} if a value is present, otherwise {@code false}
128 */
129 public boolean isPresent() {
130 return isPresent;
131 }
132
133 /**
134 * If a value is present, performs the given action with the value,
135 * otherwise does nothing.
136 *
137 * @param action the action to be performed, if a value is present
138 * @throws NullPointerException if value is present and the given action is
139 * {@code null}
140 */
141 public void ifPresent(IntConsumer action) {
142 if (isPresent) {
143 action.accept(value);
144 }
145 }
146
147 /**
148 * If a value is present, performs the given action with the value,
149 * otherwise performs the given empty-based action.
150 *
151 * @param action the action to be performed, if a value is present
152 * @param emptyAction the empty-based action to be performed, if no value is
153 * present
154 * @throws NullPointerException if a value is present and the given action
155 * is {@code null}, or no value is present and the given empty-based
156 * action is {@code null}.
157 * @since 9
158 */
159 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
160 if (isPresent) {
161 action.accept(value);
162 } else {
163 emptyAction.run();
164 }
165 }
166
167 /**
168 * If a value is present, returns a sequential {@link IntStream} containing
169 * only that value, otherwise returns an empty {@code IntStream}.
170 *
171 * @apiNote
172 * This method can be used to transform a {@code Stream} of optional
173 * integers to an {@code IntStream} of present integers:
174 * <pre>{@code
175 * Stream<OptionalInt> os = ..
176 * IntStream s = os.flatMapToInt(OptionalInt::stream)
177 * }</pre>
178 *
179 * @return the optional value as an {@code IntStream}
180 * @since 9
181 */
182 public IntStream stream() {
183 if (isPresent) {
184 return IntStream.of(value);
185 } else {
186 return IntStream.empty();
187 }
188 }
189
190 /**
191 * If a value is present, returns the value, otherwise returns
192 * {@code other}.
193 *
194 * @param other the value to be returned, if no value is present
195 * @return the value, if present, otherwise {@code other}
196 */
197 public int orElse(int other) {
198 return isPresent ? value : other;
199 }
200
201 /**
202 * If a value is present, returns the value, otherwise returns the result
203 * produced by the supplying function.
204 *
205 * @param supplier the supplying function that produces a value to be returned
206 * @return the value, if present, otherwise the result produced by the
207 * supplying function
208 * @throws NullPointerException if no value is present and the supplying
209 * function is {@code null}
210 */
211 public int orElseGet(IntSupplier supplier) {
212 return isPresent ? value : supplier.getAsInt();
213 }
214
215 /**
216 * If a value is present, returns the value, otherwise throws an exception
217 * produced by the exception supplying function.
218 *
219 * @apiNote
220 * A method reference to the exception constructor with an empty argument
221 * list can be used as the supplier. For example,
222 * {@code IllegalStateException::new}
223 *
224 * @param <X> Type of the exception to be thrown
225 * @param exceptionSupplier the supplying function that produces an
226 * exception to be thrown
227 * @return the value, if present
228 * @throws X if no value is present
229 * @throws NullPointerException if no value is present and the exception
230 * supplying function is {@code null}
231 */
232 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
233 if (isPresent) {
234 return value;
235 } else {
236 throw exceptionSupplier.get();
237 }
238 }
239
240 /**
241 * Indicates whether some other object is "equal to" this
242 * {@code OptionalInt}. The other object is considered equal if:
243 * <ul>
244 * <li>it is also an {@code OptionalInt} and;
245 * <li>both instances have no value present or;
246 * <li>the present values are "equal to" each other via {@code ==}.
247 * </ul>
248 *
249 * @param obj an object to be tested for equality
250 * @return {@code true} if the other object is "equal to" this object
251 * otherwise {@code false}
252 */
253 @Override
254 public boolean equals(Object obj) {
255 if (this == obj) {
256 return true;
257 }
258
259 if (!(obj instanceof OptionalInt)) {
260 return false;
261 }
262
263 OptionalInt other = (OptionalInt) obj;
264 return (isPresent && other.isPresent)
265 ? value == other.value
266 : isPresent == other.isPresent;
267 }
268
269 /**
270 * Returns the hash code of the value, if present, otherwise {@code 0}
271 * (zero) if no value is present.
272 *
273 * @return hash code value of the present value or {@code 0} if no value is
274 * present
275 */
276 @Override
277 public int hashCode() {
278 return isPresent ? Integer.hashCode(value) : 0;
279 }
280
281 /**
282 * Returns a non-empty string representation of this {@code OptionalInt}
283 * suitable for debugging. The exact presentation format is unspecified and
284 * may vary between implementations and versions.
285 *
286 * @implSpec
287 * If a value is present the result must include its string representation
288 * in the result. Empty and present {@code OptionalInt}s must be
289 * unambiguously differentiable.
290 *
291 * @return the string representation of this instance
292 */
293 @Override
294 public String toString() {
295 return isPresent
296 ? String.format("OptionalInt[%s]", value)
297 : "OptionalInt.empty";
298 }
299 }