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 * Equivalent to {@link #getWhenPresent()}.
111 * If a value is present, returns the value, otherwise throws
112 * {@code NoSuchElementException}.
113 *
114 * @deprecated
115 * This method's name {@code getAsInt} makes it the obvious method to
116 * call to retrieve the value from this {@code OptionalInt}. However, it has
117 * no mechanism to avoid an exception if this {@code OptionalInt} is empty.
118 * This tends to lead to code that mishandles empty {@code OptionalInt}
119 * values. Consider using other methods that handle the case where
120 * the {@code OptionalInt} might be empty, such as
121 * {@link #ifPresent(java.util.function.IntConsumer) ifPresent()}
122 * and related methods, and
123 * {@link #orElse(int) orElse()} and related methods.
124 * Use {@link getWhenPresent()} when it is known that a value is
125 * always present.
126 *
127 * @return the value described by this {@code OptionalInt}
128 * @throws NoSuchElementException if no value is present
129 * @see OptionalInt#isPresent()
130 */
131 @Deprecated(since="9")
132 public int getAsInt() {
133 return getWhenPresent();
134 }
135
136 /**
137 * If a value is present, returns the value, otherwise throws
138 * {@code NoSuchElementException}.
139 *
140 * @apiNote
141 * Use this method only when it is known that a value is always present.
142 *
143 * @return the value described by this {@code OptionalInt}
144 * @throws NoSuchElementException if no value is present
145 * @see OptionalInt#isPresent()
146 */
147 public int getWhenPresent() {
148 if (!isPresent) {
149 throw new NoSuchElementException("No value present");
150 }
151 return value;
152 }
153
154 /**
155 * If a value is present, returns {@code true}, otherwise {@code false}.
156 *
157 * @return {@code true} if a value is present, otherwise {@code false}
158 */
159 public boolean isPresent() {
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 an exception
247 * produced by the exception supplying function.
248 *
249 * @apiNote
250 * A method reference to the exception constructor with an empty argument
251 * list can be used as the supplier. For example,
252 * {@code IllegalStateException::new}
253 *
254 * @param <X> Type of the exception to be thrown
255 * @param exceptionSupplier the supplying function that produces an
256 * exception to be thrown
257 * @return the value, if present
258 * @throws X if no value is present
259 * @throws NullPointerException if no value is present and the exception
260 * supplying function is {@code null}
261 */
262 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
263 if (isPresent) {
264 return value;
265 } else {
266 throw exceptionSupplier.get();
267 }
268 }
269
270 /**
271 * Indicates whether some other object is "equal to" this
272 * {@code OptionalInt}. The other object is considered equal if:
273 * <ul>
274 * <li>it is also an {@code OptionalInt} and;
275 * <li>both instances have no value present or;
276 * <li>the present values are "equal to" each other via {@code ==}.
277 * </ul>
278 *
279 * @param obj an object to be tested for equality
280 * @return {@code true} if the other object is "equal to" this object
281 * otherwise {@code false}
282 */
283 @Override
284 public boolean equals(Object obj) {
285 if (this == obj) {
286 return true;
287 }
288
289 if (!(obj instanceof OptionalInt)) {
290 return false;
291 }
292
293 OptionalInt other = (OptionalInt) obj;
294 return (isPresent && other.isPresent)
295 ? value == other.value
296 : isPresent == other.isPresent;
297 }
298
299 /**
300 * Returns the hash code of the value, if present, otherwise {@code 0}
301 * (zero) if no value is present.
302 *
303 * @return hash code value of the present value or {@code 0} if no value is
304 * present
305 */
306 @Override
307 public int hashCode() {
308 return isPresent ? Integer.hashCode(value) : 0;
309 }
310
311 /**
312 * Returns a non-empty string representation of this {@code OptionalInt}
313 * suitable for debugging. The exact presentation format is unspecified and
314 * may vary between implementations and versions.
315 *
316 * @implSpec
317 * If a value is present the result must include its string representation
318 * in the result. Empty and present {@code OptionalInt}s must be
319 * unambiguously differentiable.
320 *
321 * @return the string representation of this instance
322 */
323 @Override
324 public String toString() {
325 return isPresent
326 ? String.format("OptionalInt[%s]", value)
327 : "OptionalInt.empty";
328 }
329 }