1 /*
2 * Copyright (c) 2012, 2020, 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
22 * or visit www.oracle.com if you need additional information or have any
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.
34 * If a value is present, {@code isPresent()} returns {@code true}. If no
35 * value is present, the object is considered <i>empty</i> and
36 * {@code isPresent()} returns {@code false}.
37 *
38 * <p>Additional methods that depend on the presence or absence of a contained
39 * value are provided, such as {@link #orElse(int) orElse()}
40 * (returns a default value if no value is present) and
41 * {@link #ifPresent(IntConsumer) ifPresent()} (performs an
42 * action if a value is present).
43 *
44 * <p>This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
45 * class; programmers should treat instances that are {@linkplain #equals(Object) equal} 46 * as interchangeable and should not use instances for synchronization, mutexes, or 47 * with {@linkplain java.lang.ref.Reference object references}. 48 * 49 * <div class="preview-block"> 50 * <div class="preview-comment"> 51 * When preview features are enabled, {@code OptionalInt} is a {@linkplain Class#isValue value class}. 52 * Use of value class instances for synchronization, mutexes, or with 53 * {@linkplain java.lang.ref.Reference object references} result in 54 * {@link IdentityException}. 55 * </div> 56 * </div>
57 *
58 * @apiNote
59 * {@code OptionalInt} is primarily intended for use as a method return type where
60 * there is a clear need to represent "no result." A variable whose type is
61 * {@code OptionalInt} should never itself be {@code null}; it should always point
62 * to an {@code OptionalInt} instance.
63 *
64 * @since 1.8
65 */
66 @jdk.internal.ValueBased
67 public final /*value*/ class OptionalInt {
68 /**
69 * Common instance for {@code empty()}.
70 */
71 private static final OptionalInt EMPTY = new OptionalInt();
72
73 /**
74 * If true then the value is present, otherwise indicates no value is present
75 */
76 private final boolean isPresent;
77 private final int value;
78
79 /**
80 * Construct an empty instance.
81 *
82 * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
83 * should exist per VM.
84 */
85 private OptionalInt() {
86 this.isPresent = false;
87 this.value = 0;
88 }
89
90 /**
91 * Returns an empty {@code OptionalInt} instance. No value is present for
92 * this {@code OptionalInt}.
93 *
94 * @apiNote
95 * Though it may be tempting to do so, avoid testing if an object is empty
96 * by comparing with {@code ==} or {@code !=} against instances returned by
97 * {@code OptionalInt.empty()}. There is no guarantee that it is a singleton.
98 * Instead, use {@link #isEmpty()} or {@link #isPresent()}.
99 *
100 * @return an empty {@code OptionalInt}
101 */
102 public static OptionalInt empty() {
103 return EMPTY;
104 }
105
106 /**
107 * Construct an instance with the described value.
108 *
109 * @param value the int value to describe
110 */
111 private OptionalInt(int value) {
112 this.isPresent = true;
113 this.value = value;
114 }
115
116 /**
117 * Returns an {@code OptionalInt} describing the given value.
118 *
119 * @param value the value to describe
120 * @return an {@code OptionalInt} with the value present
121 */
122 public static OptionalInt of(int value) {
123 return new OptionalInt(value);
124 }
125
126 /**
127 * If a value is present, returns the value, otherwise throws
128 * {@code NoSuchElementException}.
129 *
130 * @apiNote
131 * The preferred alternative to this method is {@link #orElseThrow()}.
132 *
133 * @return the value described by this {@code OptionalInt}
134 * @throws NoSuchElementException if no value is present
135 */
136 public int getAsInt() {
137 if (!isPresent) {
138 throw new NoSuchElementException("No value present");
139 }
140 return value;
141 }
142
143 /**
144 * If a value is present, returns {@code true}, otherwise {@code false}.
145 *
146 * @return {@code true} if a value is present, otherwise {@code false}
147 */
148 public boolean isPresent() {
149 return isPresent;
150 }
151
152 /**
153 * If a value is not present, returns {@code true}, otherwise
154 * {@code false}.
155 *
156 * @return {@code true} if a value is not present, otherwise {@code false}
157 * @since 11
158 */
159 public boolean isEmpty() {
160 return !isPresent;
161 }
162
163 /**
164 * If a value is present, performs the given action with the value,
165 * otherwise does nothing.
166 *
167 * @param action the action to be performed, if a value is present
168 * @throws NullPointerException if value is present and the given action is
169 * {@code null}
170 */
171 public void ifPresent(IntConsumer action) {
172 if (isPresent) {
173 action.accept(value);
174 }
175 }
176
177 /**
178 * If a value is present, performs the given action with the value,
179 * otherwise performs the given empty-based action.
180 *
181 * @param action the action to be performed, if a value is present
182 * @param emptyAction the empty-based action to be performed, if no value is
183 * present
184 * @throws NullPointerException if a value is present and the given action
185 * is {@code null}, or no value is present and the given empty-based
186 * action is {@code null}.
187 * @since 9
188 */
189 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
190 if (isPresent) {
191 action.accept(value);
192 } else {
193 emptyAction.run();
194 }
195 }
196
197 /**
198 * If a value is present, returns a sequential {@link IntStream} containing
199 * only that value, otherwise returns an empty {@code IntStream}.
200 *
201 * @apiNote
202 * This method can be used to transform a {@code Stream} of optional
203 * integers to an {@code IntStream} of present integers:
204 * <pre>{@code
205 * Stream<OptionalInt> os = ..
206 * IntStream s = os.flatMapToInt(OptionalInt::stream)
207 * }</pre>
208 *
209 * @return the optional value as an {@code IntStream}
210 * @since 9
211 */
212 public IntStream stream() {
213 if (isPresent) {
214 return IntStream.of(value);
215 } else {
216 return IntStream.empty();
217 }
218 }
219
220 /**
221 * If a value is present, returns the value, otherwise returns
222 * {@code other}.
223 *
224 * @param other the value to be returned, if no value is present
225 * @return the value, if present, otherwise {@code other}
226 */
227 public int orElse(int other) {
228 return isPresent ? value : other;
229 }
230
231 /**
232 * If a value is present, returns the value, otherwise returns the result
233 * produced by the supplying function.
234 *
235 * @param supplier the supplying function that produces a value to be returned
236 * @return the value, if present, otherwise the result produced by the
237 * supplying function
238 * @throws NullPointerException if no value is present and the supplying
239 * function is {@code null}
240 */
241 public int orElseGet(IntSupplier supplier) {
242 return isPresent ? value : supplier.getAsInt();
243 }
244
245 /**
246 * If a value is present, returns the value, otherwise throws
247 * {@code NoSuchElementException}.
248 *
249 * @return the value described by this {@code OptionalInt}
250 * @throws NoSuchElementException if no value is present
251 * @since 10
252 */
253 public int orElseThrow() {
254 if (!isPresent) {
255 throw new NoSuchElementException("No value present");
256 }
257 return value;
258 }
259
260 /**
261 * If a value is present, returns the value, otherwise throws an exception
262 * produced by the exception supplying function.
263 *
264 * @apiNote
265 * A method reference to the exception constructor with an empty argument
266 * list can be used as the supplier. For example,
267 * {@code IllegalStateException::new}
268 *
269 * @param <X> Type of the exception to be thrown
270 * @param exceptionSupplier the supplying function that produces an
271 * exception to be thrown
272 * @return the value, if present
273 * @throws X if no value is present
274 * @throws NullPointerException if no value is present and the exception
275 * supplying function is {@code null}
276 */
277 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
278 if (isPresent) {
279 return value;
280 } else {
281 throw exceptionSupplier.get();
282 }
283 }
284
285 /**
286 * Indicates whether some other object is "equal to" this
287 * {@code OptionalInt}. The other object is considered equal if:
288 * <ul>
289 * <li>it is also an {@code OptionalInt} and;
290 * <li>both instances have no value present or;
291 * <li>the present values are "equal to" each other via {@code ==}.
292 * </ul>
293 *
294 * @param obj an object to be tested for equality
295 * @return {@code true} if the other object is "equal to" this object
296 * otherwise {@code false}
297 */
298 @Override
299 public boolean equals(Object obj) {
300 if (this == obj) {
301 return true;
302 }
303
304 return obj instanceof OptionalInt other
305 && (isPresent && other.isPresent
306 ? value == other.value
307 : isPresent == other.isPresent);
308 }
309
310 /**
311 * Returns the hash code of the value, if present, otherwise {@code 0}
312 * (zero) if no value is present.
313 *
314 * @return hash code value of the present value or {@code 0} if no value is
315 * present
316 */
317 @Override
318 public int hashCode() {
319 return isPresent ? Integer.hashCode(value) : 0;
320 }
321
322 /**
323 * Returns a non-empty string representation of this {@code OptionalInt}
324 * suitable for debugging. The exact presentation format is unspecified and
325 * may vary between implementations and versions.
326 *
327 * @implSpec
328 * If a value is present the result must include its string representation
329 * in the result. Empty and present {@code OptionalInt}s must be
330 * unambiguously differentiable.
331 *
332 * @return the string representation of this instance
333 */
334 @Override
335 public String toString() {
336 return isPresent
337 ? ("OptionalInt[" + value + "]")
338 : "OptionalInt.empty";
339 }
340 }
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