1 /*
2 * Copyright (c) 2012, 2017, 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(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 * @apiNote
49 * {@code OptionalInt} is primarily intended for use as a method return type where
50 * there is a clear need to represent "no result." A variable whose type is
51 * {@code OptionalInt} should never itself be {@code null}; it should always point
52 * to an {@code OptionalInt} instance.
53 *
54 * @since 1.8
55 */
56 public final class OptionalInt {
57 /**
58 * Common instance for {@code empty()}.
59 */
60 private static final OptionalInt EMPTY = new OptionalInt();
61
62 /**
63 * If true then the value is present, otherwise indicates no value is present
64 */
65 private final boolean isPresent;
66 private final int value;
67
68 /**
69 * Construct an empty instance.
70 *
71 * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
72 * should exist per VM.
73 */
74 private OptionalInt() {
75 this.isPresent = false;
76 this.value = 0;
77 }
78
79 /**
80 * Returns an empty {@code OptionalInt} instance. No value is present for
81 * this {@code OptionalInt}.
82 *
83 * @apiNote
84 * Though it may be tempting to do so, avoid testing if an object is empty
85 * by comparing with {@code ==} against instances returned by
86 * {@code OptionalInt.empty()}. There is no guarantee that it is a singleton.
87 * Instead, use {@link #isPresent()}.
88 *
89 * @return an empty {@code OptionalInt}
90 */
91 public static OptionalInt empty() {
92 return EMPTY;
93 }
94
95 /**
96 * Construct an instance with the described value.
97 *
98 * @param value the int value to describe
99 */
100 private OptionalInt(int value) {
101 this.isPresent = true;
102 this.value = value;
103 }
104
105 /**
106 * Returns an {@code OptionalInt} describing the given value.
107 *
108 * @param value the value to describe
109 * @return an {@code OptionalInt} with the value present
110 */
111 public static OptionalInt of(int value) {
112 return new OptionalInt(value);
113 }
114
115 /**
116 * If a value is present, returns the value, otherwise throws
117 * {@code NoSuchElementException}.
118 *
119 * @apiNote
120 * The preferred alternative to this method is {@link #orElseThrow()}.
121 *
122 * @return the value described by this {@code OptionalInt}
123 * @throws NoSuchElementException if no value is present
124 */
125 public int getAsInt() {
126 if (!isPresent) {
127 throw new NoSuchElementException("No value present");
128 }
129 return value;
130 }
131
132 /**
133 * If a value is present, returns {@code true}, otherwise {@code false}.
134 *
135 * @return {@code true} if a value is present, otherwise {@code false}
136 */
137 public boolean isPresent() {
138 return isPresent;
139 }
140
141 /**
142 * If a value is present, performs the given action with the value,
143 * otherwise does nothing.
144 *
145 * @param action the action to be performed, if a value is present
146 * @throws NullPointerException if value is present and the given action is
147 * {@code null}
148 */
149 public void ifPresent(IntConsumer action) {
150 if (isPresent) {
151 action.accept(value);
152 }
153 }
154
155 /**
156 * If a value is present, performs the given action with the value,
157 * otherwise performs the given empty-based action.
158 *
159 * @param action the action to be performed, if a value is present
160 * @param emptyAction the empty-based action to be performed, if no value is
161 * present
162 * @throws NullPointerException if a value is present and the given action
163 * is {@code null}, or no value is present and the given empty-based
164 * action is {@code null}.
165 * @since 9
166 */
167 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
168 if (isPresent) {
169 action.accept(value);
170 } else {
171 emptyAction.run();
172 }
173 }
174
175 /**
176 * If a value is present, returns a sequential {@link IntStream} containing
177 * only that value, otherwise returns an empty {@code IntStream}.
178 *
179 * @apiNote
180 * This method can be used to transform a {@code Stream} of optional
181 * integers to an {@code IntStream} of present integers:
182 * <pre>{@code
183 * Stream<OptionalInt> os = ..
184 * IntStream s = os.flatMapToInt(OptionalInt::stream)
185 * }</pre>
186 *
187 * @return the optional value as an {@code IntStream}
188 * @since 9
189 */
190 public IntStream stream() {
191 if (isPresent) {
192 return IntStream.of(value);
193 } else {
194 return IntStream.empty();
195 }
196 }
197
198 /**
199 * If a value is present, returns the value, otherwise returns
200 * {@code other}.
201 *
202 * @param other the value to be returned, if no value is present
203 * @return the value, if present, otherwise {@code other}
204 */
205 public int orElse(int other) {
206 return isPresent ? value : other;
207 }
208
209 /**
210 * If a value is present, returns the value, otherwise returns the result
211 * produced by the supplying function.
212 *
213 * @param supplier the supplying function that produces a value to be returned
214 * @return the value, if present, otherwise the result produced by the
215 * supplying function
216 * @throws NullPointerException if no value is present and the supplying
217 * function is {@code null}
218 */
219 public int orElseGet(IntSupplier supplier) {
220 return isPresent ? value : supplier.getAsInt();
221 }
222
223 /**
224 * If a value is present, returns the value, otherwise throws
225 * {@code NoSuchElementException}.
226 *
227 * @return the value described by this {@code OptionalInt}
228 * @throws NoSuchElementException if no value is present
229 * @since 10
230 */
231 public int orElseThrow() {
232 if (!isPresent) {
233 throw new NoSuchElementException("No value present");
234 }
235 return value;
236 }
237
238 /**
239 * If a value is present, returns the value, otherwise throws an exception
240 * produced by the exception supplying function.
241 *
242 * @apiNote
243 * A method reference to the exception constructor with an empty argument
244 * list can be used as the supplier. For example,
245 * {@code IllegalStateException::new}
246 *
247 * @param <X> Type of the exception to be thrown
248 * @param exceptionSupplier the supplying function that produces an
249 * exception to be thrown
250 * @return the value, if present
251 * @throws X if no value is present
252 * @throws NullPointerException if no value is present and the exception
253 * supplying function is {@code null}
254 */
255 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
256 if (isPresent) {
257 return value;
258 } else {
259 throw exceptionSupplier.get();
260 }
261 }
262
263 /**
264 * Indicates whether some other object is "equal to" this
265 * {@code OptionalInt}. The other object is considered equal if:
266 * <ul>
267 * <li>it is also an {@code OptionalInt} and;
268 * <li>both instances have no value present or;
269 * <li>the present values are "equal to" each other via {@code ==}.
270 * </ul>
271 *
272 * @param obj an object to be tested for equality
273 * @return {@code true} if the other object is "equal to" this object
274 * otherwise {@code false}
275 */
276 @Override
277 public boolean equals(Object obj) {
278 if (this == obj) {
279 return true;
280 }
281
282 if (!(obj instanceof OptionalInt)) {
283 return false;
284 }
285
286 OptionalInt other = (OptionalInt) obj;
287 return (isPresent && other.isPresent)
288 ? value == other.value
289 : isPresent == other.isPresent;
290 }
291
292 /**
293 * Returns the hash code of the value, if present, otherwise {@code 0}
294 * (zero) if no value is present.
295 *
296 * @return hash code value of the present value or {@code 0} if no value is
297 * present
298 */
299 @Override
300 public int hashCode() {
301 return isPresent ? Integer.hashCode(value) : 0;
302 }
303
304 /**
305 * Returns a non-empty string representation of this {@code OptionalInt}
306 * suitable for debugging. The exact presentation format is unspecified and
307 * may vary between implementations and versions.
308 *
309 * @implSpec
310 * If a value is present the result must include its string representation
311 * in the result. Empty and present {@code OptionalInt}s must be
312 * unambiguously differentiable.
313 *
314 * @return the string representation of this instance
315 */
316 @Override
317 public String toString() {
318 return isPresent
319 ? String.format("OptionalInt[%s]", value)
320 : "OptionalInt.empty";
321 }
322 }