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
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23 * questions.
24 */
25 package java.util;
26
27 import java.util.function.LongConsumer;
28 import java.util.function.LongSupplier;
29 import java.util.function.Supplier;
30 import java.util.stream.LongStream;
31
32 /**
33 * A container object which may or may not contain a {@code long} 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(long) orElse()}
40 * (returns a default value if no value is present) and
41 * {@link #ifPresent(LongConsumer) 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
46 * {@linkplain #equals(Object) equal} as interchangeable and should not
47 * use instances for synchronization, or unpredictable behavior may
48 * occur. For example, in a future release, synchronization may fail.
49 *
50 * @apiNote
51 * {@code OptionalLong} is primarily intended for use as a method return type where
52 * there is a clear need to represent "no result." A variable whose type is
53 * {@code OptionalLong} should never itself be {@code null}; it should always point
54 * to an {@code OptionalLong} instance.
55 *
56 * @since 1.8
57 */
58 @jdk.internal.ValueBased
59 public final class OptionalLong {
60 /**
61 * Common instance for {@code empty()}.
62 */
63 private static final OptionalLong EMPTY = new OptionalLong();
64
65 /**
66 * If true then the value is present, otherwise indicates no value is present
67 */
68 private final boolean isPresent;
69 private final long value;
70
71 /**
72 * Construct an empty instance.
73 *
74 * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
75 * should exist per VM.
76 */
77 private OptionalLong() {
78 this.isPresent = false;
79 this.value = 0;
80 }
81
82 /**
83 * Returns an empty {@code OptionalLong} instance. No value is present for
84 * this {@code OptionalLong}.
85 *
86 * @apiNote
87 * Though it may be tempting to do so, avoid testing if an object is empty
88 * by comparing with {@code ==} or {@code !=} against instances returned by
89 * {@code OptionalLong.empty()}. There is no guarantee that it is a singleton.
90 * Instead, use {@link #isEmpty()} or {@link #isPresent()}.
91 *
92 * @return an empty {@code OptionalLong}.
93 */
94 public static OptionalLong empty() {
95 return EMPTY;
96 }
97
98 /**
99 * Construct an instance with the described value.
100 *
101 * @param value the long value to describe
102 */
103 private OptionalLong(long value) {
104 this.isPresent = true;
105 this.value = value;
106 }
107
108 /**
109 * Returns an {@code OptionalLong} describing the given value.
110 *
111 * @param value the value to describe
112 * @return an {@code OptionalLong} with the value present
113 */
114 public static OptionalLong of(long value) {
115 return new OptionalLong(value);
116 }
117
118 /**
119 * If a value is present, returns the value, otherwise throws
120 * {@code NoSuchElementException}.
121 *
122 * @apiNote
123 * The preferred alternative to this method is {@link #orElseThrow()}.
124 *
125 * @return the value described by this {@code OptionalLong}
126 * @throws NoSuchElementException if no value is present
127 */
128 public long getAsLong() {
129 if (!isPresent) {
130 throw new NoSuchElementException("No value present");
131 }
132 return value;
133 }
134
135 /**
136 * If a value is present, returns {@code true}, otherwise {@code false}.
137 *
138 * @return {@code true} if a value is present, otherwise {@code false}
139 */
140 public boolean isPresent() {
141 return isPresent;
142 }
143
144 /**
145 * If a value is not present, returns {@code true}, otherwise
146 * {@code false}.
147 *
148 * @return {@code true} if a value is not present, otherwise {@code false}
149 * @since 11
150 */
151 public boolean isEmpty() {
152 return !isPresent;
153 }
154
155 /**
156 * If a value is present, performs the given action with the value,
157 * otherwise does nothing.
158 *
159 * @param action the action to be performed, if a value is present
160 * @throws NullPointerException if value is present and the given action is
161 * {@code null}
162 */
163 public void ifPresent(LongConsumer action) {
164 if (isPresent) {
165 action.accept(value);
166 }
167 }
168
169 /**
170 * If a value is present, performs the given action with the value,
171 * otherwise performs the given empty-based action.
172 *
173 * @param action the action to be performed, if a value is present
174 * @param emptyAction the empty-based action to be performed, if no value is
175 * present
176 * @throws NullPointerException if a value is present and the given action
177 * is {@code null}, or no value is present and the given empty-based
178 * action is {@code null}.
179 * @since 9
180 */
181 public void ifPresentOrElse(LongConsumer action, Runnable emptyAction) {
182 if (isPresent) {
183 action.accept(value);
184 } else {
185 emptyAction.run();
186 }
187 }
188
189 /**
190 * If a value is present, returns a sequential {@link LongStream} containing
191 * only that value, otherwise returns an empty {@code LongStream}.
192 *
193 * @apiNote
194 * This method can be used to transform a {@code Stream} of optional longs
195 * to an {@code LongStream} of present longs:
196 * <pre>{@code
197 * Stream<OptionalLong> os = ..
198 * LongStream s = os.flatMapToLong(OptionalLong::stream)
199 * }</pre>
200 *
201 * @return the optional value as an {@code LongStream}
202 * @since 9
203 */
204 public LongStream stream() {
205 if (isPresent) {
206 return LongStream.of(value);
207 } else {
208 return LongStream.empty();
209 }
210 }
211
212 /**
213 * If a value is present, returns the value, otherwise returns
214 * {@code other}.
215 *
216 * @param other the value to be returned, if no value is present
217 * @return the value, if present, otherwise {@code other}
218 */
219 public long orElse(long other) {
220 return isPresent ? value : other;
221 }
222
223 /**
224 * If a value is present, returns the value, otherwise returns the result
225 * produced by the supplying function.
226 *
227 * @param supplier the supplying function that produces a value to be returned
228 * @return the value, if present, otherwise the result produced by the
229 * supplying function
230 * @throws NullPointerException if no value is present and the supplying
231 * function is {@code null}
232 */
233 public long orElseGet(LongSupplier supplier) {
234 return isPresent ? value : supplier.getAsLong();
235 }
236
237 /**
238 * If a value is present, returns the value, otherwise throws
239 * {@code NoSuchElementException}.
240 *
241 * @return the value described by this {@code OptionalLong}
242 * @throws NoSuchElementException if no value is present
243 * @since 10
244 */
245 public long orElseThrow() {
246 if (!isPresent) {
247 throw new NoSuchElementException("No value present");
248 }
249 return value;
250 }
251
252 /**
253 * If a value is present, returns the value, otherwise throws an exception
254 * produced by the exception supplying function.
255 *
256 * @apiNote
257 * A method reference to the exception constructor with an empty argument
258 * list can be used as the supplier. For example,
259 * {@code IllegalStateException::new}
260 *
261 * @param <X> Type of the exception to be thrown
262 * @param exceptionSupplier the supplying function that produces an
263 * exception to be thrown
264 * @return the value, if present
265 * @throws X if no value is present
266 * @throws NullPointerException if no value is present and the exception
267 * supplying function is {@code null}
268 */
269 public<X extends Throwable> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
270 if (isPresent) {
271 return value;
272 } else {
273 throw exceptionSupplier.get();
274 }
275 }
276
277 /**
278 * Indicates whether some other object is "equal to" this
279 * {@code OptionalLong}. The other object is considered equal if:
280 * <ul>
281 * <li>it is also an {@code OptionalLong} and;
282 * <li>both instances have no value present or;
283 * <li>the present values are "equal to" each other via {@code ==}.
284 * </ul>
285 *
286 * @param obj an object to be tested for equality
287 * @return {@code true} if the other object is "equal to" this object
288 * otherwise {@code false}
289 */
290 @Override
291 public boolean equals(Object obj) {
292 if (this == obj) {
293 return true;
294 }
295
296 return obj instanceof OptionalLong other
297 && (isPresent && other.isPresent
298 ? value == other.value
299 : isPresent == other.isPresent);
300 }
301
302 /**
303 * Returns the hash code of the value, if present, otherwise {@code 0}
304 * (zero) if no value is present.
305 *
306 * @return hash code value of the present value or {@code 0} if no value is
307 * present
308 */
309 @Override
310 public int hashCode() {
311 return isPresent ? Long.hashCode(value) : 0;
312 }
313
314 /**
315 * Returns a non-empty string representation of this {@code OptionalLong}
316 * suitable for debugging. The exact presentation format is unspecified and
317 * may vary between implementations and versions.
318 *
319 * @implSpec
320 * If a value is present the result must include its string representation
321 * in the result. Empty and present {@code OptionalLong}s must be
322 * unambiguously differentiable.
323 *
324 * @return the string representation of this instance
325 */
326 @Override
327 public String toString() {
328 return isPresent
329 ? ("OptionalLong[" + value + "]")
330 : "OptionalLong.empty";
331 }
332 }