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.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="../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 OptionalLong} may have unpredictable results and should be avoided.
48 *
49 * @apiNote
50 * {@code OptionalLong} 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 OptionalLong} should never itself be {@code null}; it should always point
53 * to an {@code OptionalLong} instance.
54 *
55 * @since 1.8
56 */
57 public final class OptionalLong {
58 /**
59 * Common instance for {@code empty()}.
60 */
61 private static final OptionalLong EMPTY = new OptionalLong();
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 long value;
68
69 /**
70 * Construct an empty instance.
71 *
72 * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
73 * should exist per VM.
74 */
75 private OptionalLong() {
76 this.isPresent = false;
77 this.value = 0;
78 }
79
80 /**
81 * Returns an empty {@code OptionalLong} instance. No value is present for
82 * this {@code OptionalLong}.
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 OptionalLong.empty()}. There is no guarantee that it is a singleton.
88 * Instead, use {@link #isPresent()}.
89 *
90 * @return an empty {@code OptionalLong}.
91 */
92 public static OptionalLong empty() {
93 return EMPTY;
94 }
95
96 /**
97 * Construct an instance with the described value.
98 *
99 * @param value the long value to describe
100 */
101 private OptionalLong(long value) {
102 this.isPresent = true;
103 this.value = value;
104 }
105
106 /**
107 * Returns an {@code OptionalLong} describing the given value.
108 *
109 * @param value the value to describe
110 * @return an {@code OptionalLong} with the value present
111 */
112 public static OptionalLong of(long value) {
113 return new OptionalLong(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 OptionalLong}
124 * @throws NoSuchElementException if no value is present
125 */
126 public long getAsLong() {
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 */
148 public boolean isEmpty() {
149 return !isPresent;
150 }
151
152 /**
153 * If a value is present, performs the given action with the value,
154 * otherwise does nothing.
155 *
156 * @param action the action to be performed, if a value is present
157 * @throws NullPointerException if value is present and the given action is
158 * {@code null}
159 */
160 public void ifPresent(LongConsumer action) {
161 if (isPresent) {
162 action.accept(value);
163 }
164 }
165
166 /**
167 * If a value is present, performs the given action with the value,
168 * otherwise performs the given empty-based action.
169 *
170 * @param action the action to be performed, if a value is present
171 * @param emptyAction the empty-based action to be performed, if no value is
172 * present
173 * @throws NullPointerException if a value is present and the given action
174 * is {@code null}, or no value is present and the given empty-based
175 * action is {@code null}.
176 * @since 9
177 */
178 public void ifPresentOrElse(LongConsumer action, Runnable emptyAction) {
179 if (isPresent) {
180 action.accept(value);
181 } else {
182 emptyAction.run();
183 }
184 }
185
186 /**
187 * If a value is present, returns a sequential {@link LongStream} containing
188 * only that value, otherwise returns an empty {@code LongStream}.
189 *
190 * @apiNote
191 * This method can be used to transform a {@code Stream} of optional longs
192 * to an {@code LongStream} of present longs:
193 * <pre>{@code
194 * Stream<OptionalLong> os = ..
195 * LongStream s = os.flatMapToLong(OptionalLong::stream)
196 * }</pre>
197 *
198 * @return the optional value as an {@code LongStream}
199 * @since 9
200 */
201 public LongStream stream() {
202 if (isPresent) {
203 return LongStream.of(value);
204 } else {
205 return LongStream.empty();
206 }
207 }
208
209 /**
210 * If a value is present, returns the value, otherwise returns
211 * {@code other}.
212 *
213 * @param other the value to be returned, if no value is present
214 * @return the value, if present, otherwise {@code other}
215 */
216 public long orElse(long other) {
217 return isPresent ? value : other;
218 }
219
220 /**
221 * If a value is present, returns the value, otherwise returns the result
222 * produced by the supplying function.
223 *
224 * @param supplier the supplying function that produces a value to be returned
225 * @return the value, if present, otherwise the result produced by the
226 * supplying function
227 * @throws NullPointerException if no value is present and the supplying
228 * function is {@code null}
229 */
230 public long orElseGet(LongSupplier supplier) {
231 return isPresent ? value : supplier.getAsLong();
232 }
233
234 /**
235 * If a value is present, returns the value, otherwise throws
236 * {@code NoSuchElementException}.
237 *
238 * @return the value described by this {@code OptionalLong}
239 * @throws NoSuchElementException if no value is present
240 * @since 10
241 */
242 public long orElseThrow() {
243 if (!isPresent) {
244 throw new NoSuchElementException("No value present");
245 }
246 return value;
247 }
248
249 /**
250 * If a value is present, returns the value, otherwise throws an exception
251 * produced by the exception supplying function.
252 *
253 * @apiNote
254 * A method reference to the exception constructor with an empty argument
255 * list can be used as the supplier. For example,
256 * {@code IllegalStateException::new}
257 *
258 * @param <X> Type of the exception to be thrown
259 * @param exceptionSupplier the supplying function that produces an
260 * exception to be thrown
261 * @return the value, if present
262 * @throws X if no value is present
263 * @throws NullPointerException if no value is present and the exception
264 * supplying function is {@code null}
265 */
266 public<X extends Throwable> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
267 if (isPresent) {
268 return value;
269 } else {
270 throw exceptionSupplier.get();
271 }
272 }
273
274 /**
275 * Indicates whether some other object is "equal to" this
276 * {@code OptionalLong}. The other object is considered equal if:
277 * <ul>
278 * <li>it is also an {@code OptionalLong} and;
279 * <li>both instances have no value present or;
280 * <li>the present values are "equal to" each other via {@code ==}.
281 * </ul>
282 *
283 * @param obj an object to be tested for equality
284 * @return {@code true} if the other object is "equal to" this object
285 * otherwise {@code false}
286 */
287 @Override
288 public boolean equals(Object obj) {
289 if (this == obj) {
290 return true;
291 }
292
293 if (!(obj instanceof OptionalLong)) {
294 return false;
295 }
296
297 OptionalLong other = (OptionalLong) obj;
298 return (isPresent && other.isPresent)
299 ? value == other.value
300 : isPresent == other.isPresent;
301 }
302
303 /**
304 * Returns the hash code of the value, if present, otherwise {@code 0}
305 * (zero) if no value is present.
306 *
307 * @return hash code value of the present value or {@code 0} if no value is
308 * present
309 */
310 @Override
311 public int hashCode() {
312 return isPresent ? Long.hashCode(value) : 0;
313 }
314
315 /**
316 * Returns a non-empty string representation of this {@code OptionalLong}
317 * suitable for debugging. The exact presentation format is unspecified and
318 * may vary between implementations and versions.
319 *
320 * @implSpec
321 * If a value is present the result must include its string representation
322 * in the result. Empty and present {@code OptionalLong}s must be
323 * unambiguously differentiable.
324 *
325 * @return the string representation of this instance
326 */
327 @Override
328 public String toString() {
329 return isPresent
330 ? String.format("OptionalLong[%s]", value)
331 : "OptionalLong.empty";
332 }
333 }