1 /*
2 * Copyright (c) 2012, 2018, 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.
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="../lang/doc-files/ValueBased.html">value-based</a>
45 * class; use of identity-sensitive operations (including reference equality
46 * ({@code ==}), identity hash code, or synchronization) on instances of
47 * {@code OptionalInt} may have unpredictable results and should be avoided.
48 *
49 * @apiNote
50 * {@code OptionalInt} is primarily intended for use as a method return type where
51 * there is a clear need to represent "no result." A variable whose type is
52 * {@code OptionalInt} should never itself be {@code null}; it should always point
53 * to an {@code OptionalInt} instance.
54 *
55 * @since 1.8
56 */
57 public final class OptionalInt {
58 /**
59 * Common instance for {@code empty()}.
60 */
61 private static final OptionalInt EMPTY = new OptionalInt();
62
63 /**
64 * If true then the value is present, otherwise indicates no value is present
65 */
66 private final boolean isPresent;
67 private final int value;
68
69 /**
70 * Construct an empty instance.
71 *
72 * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
73 * should exist per VM.
74 */
75 private OptionalInt() {
76 this.isPresent = false;
77 this.value = 0;
78 }
79
80 /**
81 * Returns an empty {@code OptionalInt} instance. No value is present for
82 * this {@code OptionalInt}.
83 *
84 * @apiNote
85 * Though it may be tempting to do so, avoid testing if an object is empty
86 * by comparing with {@code ==} against instances returned by
87 * {@code OptionalInt.empty()}. There is no guarantee that it is a singleton.
88 * Instead, use {@link #isPresent()}.
89 *
90 * @return an empty {@code OptionalInt}
91 */
92 public static OptionalInt empty() {
93 return EMPTY;
94 }
95
96 /**
97 * Construct an instance with the described value.
98 *
99 * @param value the int value to describe
100 */
101 private OptionalInt(int value) {
102 this.isPresent = true;
103 this.value = value;
104 }
105
106 /**
107 * Returns an {@code OptionalInt} describing the given value.
108 *
109 * @param value the value to describe
110 * @return an {@code OptionalInt} with the value present
111 */
112 public static OptionalInt of(int value) {
113 return new OptionalInt(value);
114 }
115
116 /**
117 * If a value is present, returns the value, otherwise throws
118 * {@code NoSuchElementException}.
119 *
120 * @apiNote
121 * The preferred alternative to this method is {@link #orElseThrow()}.
122 *
123 * @return the value described by this {@code OptionalInt}
124 * @throws NoSuchElementException if no value is present
125 */
126 public int getAsInt() {
127 if (!isPresent) {
128 throw new NoSuchElementException("No value present");
129 }
130 return value;
131 }
132
133 /**
134 * If a value is present, returns {@code true}, otherwise {@code false}.
135 *
136 * @return {@code true} if a value is present, otherwise {@code false}
137 */
138 public boolean isPresent() {
139 return isPresent;
140 }
141
142 /**
143 * If a value is not present, returns {@code true}, otherwise
144 * {@code false}.
145 *
146 * @return {@code true} if a value is not present, otherwise {@code false}
147 * @since 11
148 */
149 public boolean isEmpty() {
150 return !isPresent;
151 }
152
153 /**
154 * If a value is present, performs the given action with the value,
155 * otherwise does nothing.
156 *
157 * @param action the action to be performed, if a value is present
158 * @throws NullPointerException if value is present and the given action is
159 * {@code null}
160 */
161 public void ifPresent(IntConsumer action) {
162 if (isPresent) {
163 action.accept(value);
164 }
165 }
166
167 /**
168 * If a value is present, performs the given action with the value,
169 * otherwise performs the given empty-based action.
170 *
171 * @param action the action to be performed, if a value is present
172 * @param emptyAction the empty-based action to be performed, if no value is
173 * present
174 * @throws NullPointerException if a value is present and the given action
175 * is {@code null}, or no value is present and the given empty-based
176 * action is {@code null}.
177 * @since 9
178 */
179 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
180 if (isPresent) {
181 action.accept(value);
182 } else {
183 emptyAction.run();
184 }
185 }
186
187 /**
188 * If a value is present, returns a sequential {@link IntStream} containing
189 * only that value, otherwise returns an empty {@code IntStream}.
190 *
191 * @apiNote
192 * This method can be used to transform a {@code Stream} of optional
193 * integers to an {@code IntStream} of present integers:
194 * <pre>{@code
195 * Stream<OptionalInt> os = ..
196 * IntStream s = os.flatMapToInt(OptionalInt::stream)
197 * }</pre>
198 *
199 * @return the optional value as an {@code IntStream}
200 * @since 9
201 */
202 public IntStream stream() {
203 if (isPresent) {
204 return IntStream.of(value);
205 } else {
206 return IntStream.empty();
207 }
208 }
209
210 /**
211 * If a value is present, returns the value, otherwise returns
212 * {@code other}.
213 *
214 * @param other the value to be returned, if no value is present
215 * @return the value, if present, otherwise {@code other}
216 */
217 public int orElse(int other) {
218 return isPresent ? value : other;
219 }
220
221 /**
222 * If a value is present, returns the value, otherwise returns the result
223 * produced by the supplying function.
224 *
225 * @param supplier the supplying function that produces a value to be returned
226 * @return the value, if present, otherwise the result produced by the
227 * supplying function
228 * @throws NullPointerException if no value is present and the supplying
229 * function is {@code null}
230 */
231 public int orElseGet(IntSupplier supplier) {
232 return isPresent ? value : supplier.getAsInt();
233 }
234
235 /**
236 * If a value is present, returns the value, otherwise throws
237 * {@code NoSuchElementException}.
238 *
239 * @return the value described by this {@code OptionalInt}
240 * @throws NoSuchElementException if no value is present
241 * @since 10
242 */
243 public int orElseThrow() {
244 if (!isPresent) {
245 throw new NoSuchElementException("No value present");
246 }
247 return value;
248 }
249
250 /**
251 * If a value is present, returns the value, otherwise throws an exception
252 * produced by the exception supplying function.
253 *
254 * @apiNote
255 * A method reference to the exception constructor with an empty argument
256 * list can be used as the supplier. For example,
257 * {@code IllegalStateException::new}
258 *
259 * @param <X> Type of the exception to be thrown
260 * @param exceptionSupplier the supplying function that produces an
261 * exception to be thrown
262 * @return the value, if present
263 * @throws X if no value is present
264 * @throws NullPointerException if no value is present and the exception
265 * supplying function is {@code null}
266 */
267 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
268 if (isPresent) {
269 return value;
270 } else {
271 throw exceptionSupplier.get();
272 }
273 }
274
275 /**
276 * Indicates whether some other object is "equal to" this
277 * {@code OptionalInt}. The other object is considered equal if:
278 * <ul>
279 * <li>it is also an {@code OptionalInt} and;
280 * <li>both instances have no value present or;
281 * <li>the present values are "equal to" each other via {@code ==}.
282 * </ul>
283 *
284 * @param obj an object to be tested for equality
285 * @return {@code true} if the other object is "equal to" this object
286 * otherwise {@code false}
287 */
288 @Override
289 public boolean equals(Object obj) {
290 if (this == obj) {
291 return true;
292 }
293
294 if (!(obj instanceof OptionalInt)) {
295 return false;
296 }
297
298 OptionalInt other = (OptionalInt) obj;
299 return (isPresent && other.isPresent)
300 ? value == other.value
301 : isPresent == other.isPresent;
302 }
303
304 /**
305 * Returns the hash code of the value, if present, otherwise {@code 0}
306 * (zero) if no value is present.
307 *
308 * @return hash code value of the present value or {@code 0} if no value is
309 * present
310 */
311 @Override
312 public int hashCode() {
313 return isPresent ? Integer.hashCode(value) : 0;
314 }
315
316 /**
317 * Returns a non-empty string representation of this {@code OptionalInt}
318 * suitable for debugging. The exact presentation format is unspecified and
319 * may vary between implementations and versions.
320 *
321 * @implSpec
322 * If a value is present the result must include its string representation
323 * in the result. Empty and present {@code OptionalInt}s must be
324 * unambiguously differentiable.
325 *
326 * @return the string representation of this instance
327 */
328 @Override
329 public String toString() {
330 return isPresent
331 ? String.format("OptionalInt[%s]", value)
332 : "OptionalInt.empty";
333 }
334 }