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
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24 */
25 package java.util;
26
27 import java.util.function.DoubleConsumer;
28 import java.util.function.DoubleSupplier;
29 import java.util.function.Supplier;
30 import java.util.stream.DoubleStream;
31
32 /**
33 * A container object which may or may not contain a {@code double} 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(double) orElse()}
40 * (returns a default value if no value is present) and
41 * {@link #ifPresent(DoubleConsumer) ifPresent()} (performs
42 * an 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 OptionalDouble} 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 OptionalDouble} should never itself be {@code null}; it should always point
54 * to an {@code OptionalDouble} instance.
55 *
56 * @since 1.8
57 */
58 @jdk.internal.ValueBased
59 @jdk.internal.MigratedValueClass
60 public final class OptionalDouble {
61 /**
62 * Common instance for {@code empty()}.
63 */
64 private static final OptionalDouble EMPTY = new OptionalDouble();
65
66 /**
67 * If true then the value is present, otherwise indicates no value is present
68 */
69 private final boolean isPresent;
70 private final double value;
71
72 /**
73 * Construct an empty instance.
74 *
75 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
76 * should exist per VM.
77 */
78 private OptionalDouble() {
79 this.isPresent = false;
80 this.value = Double.NaN;
81 }
82
83 /**
84 * Returns an empty {@code OptionalDouble} instance. No value is present
85 * for this {@code OptionalDouble}.
86 *
87 * @apiNote
88 * Though it may be tempting to do so, avoid testing if an object is empty
89 * by comparing with {@code ==} or {@code !=} against instances returned by
90 * {@code OptionalDouble.empty()}. There is no guarantee that it is a singleton.
91 * Instead, use {@link #isEmpty()} or {@link #isPresent()}.
92 *
93 * @return an empty {@code OptionalDouble}.
94 */
95 public static OptionalDouble empty() {
96 return EMPTY;
97 }
98
99 /**
100 * Construct an instance with the described value.
101 *
102 * @param value the double value to describe.
103 */
104 private OptionalDouble(double value) {
105 this.isPresent = true;
106 this.value = value;
107 }
108
109 /**
110 * Returns an {@code OptionalDouble} describing the given value.
111 *
112 * @param value the value to describe
113 * @return an {@code OptionalDouble} with the value present
114 */
115 public static OptionalDouble of(double value) {
116 return new OptionalDouble(value);
117 }
118
119 /**
120 * If a value is present, returns the value, otherwise throws
121 * {@code NoSuchElementException}.
122 *
123 * @apiNote
124 * The preferred alternative to this method is {@link #orElseThrow()}.
125 *
126 * @return the value described by this {@code OptionalDouble}
127 * @throws NoSuchElementException if no value is present
128 */
129 public double getAsDouble() {
130 if (!isPresent) {
131 throw new NoSuchElementException("No value present");
132 }
133 return value;
134 }
135
136 /**
137 * If a value is present, returns {@code true}, otherwise {@code false}.
138 *
139 * @return {@code true} if a value is present, otherwise {@code false}
140 */
141 public boolean isPresent() {
142 return isPresent;
143 }
144
145 /**
146 * If a value is not present, returns {@code true}, otherwise
147 * {@code false}.
148 *
149 * @return {@code true} if a value is not present, otherwise {@code false}
150 * @since 11
151 */
152 public boolean isEmpty() {
153 return !isPresent;
154 }
155
156 /**
157 * If a value is present, performs the given action with the value,
158 * otherwise does nothing.
159 *
160 * @param action the action to be performed, if a value is present
161 * @throws NullPointerException if value is present and the given action is
162 * {@code null}
163 */
164 public void ifPresent(DoubleConsumer action) {
165 if (isPresent) {
166 action.accept(value);
167 }
168 }
169
170 /**
171 * If a value is present, performs the given action with the value,
172 * otherwise performs the given empty-based action.
173 *
174 * @param action the action to be performed, if a value is present
175 * @param emptyAction the empty-based action to be performed, if no value is
176 * present
177 * @throws NullPointerException if a value is present and the given action
178 * is {@code null}, or no value is present and the given empty-based
179 * action is {@code null}.
180 * @since 9
181 */
182 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
183 if (isPresent) {
184 action.accept(value);
185 } else {
186 emptyAction.run();
187 }
188 }
189
190 /**
191 * If a value is present, returns a sequential {@link DoubleStream}
192 * containing only that value, otherwise returns an empty
193 * {@code DoubleStream}.
194 *
195 * @apiNote
196 * This method can be used to transform a {@code Stream} of optional doubles
197 * to a {@code DoubleStream} of present doubles:
198 * <pre>{@code
199 * Stream<OptionalDouble> os = ..
200 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
201 * }</pre>
202 *
203 * @return the optional value as a {@code DoubleStream}
204 * @since 9
205 */
206 public DoubleStream stream() {
207 if (isPresent) {
208 return DoubleStream.of(value);
209 } else {
210 return DoubleStream.empty();
211 }
212 }
213
214 /**
215 * If a value is present, returns the value, otherwise returns
216 * {@code other}.
217 *
218 * @param other the value to be returned, if no value is present
219 * @return the value, if present, otherwise {@code other}
220 */
221 public double orElse(double other) {
222 return isPresent ? value : other;
223 }
224
225 /**
226 * If a value is present, returns the value, otherwise returns the result
227 * produced by the supplying function.
228 *
229 * @param supplier the supplying function that produces a value to be returned
230 * @return the value, if present, otherwise the result produced by the
231 * supplying function
232 * @throws NullPointerException if no value is present and the supplying
233 * function is {@code null}
234 */
235 public double orElseGet(DoubleSupplier supplier) {
236 return isPresent ? value : supplier.getAsDouble();
237 }
238
239 /**
240 * If a value is present, returns the value, otherwise throws
241 * {@code NoSuchElementException}.
242 *
243 * @return the value described by this {@code OptionalDouble}
244 * @throws NoSuchElementException if no value is present
245 * @since 10
246 */
247 public double orElseThrow() {
248 if (!isPresent) {
249 throw new NoSuchElementException("No value present");
250 }
251 return value;
252 }
253
254 /**
255 * If a value is present, returns the value, otherwise throws an exception
256 * produced by the exception supplying function.
257 *
258 * @apiNote
259 * A method reference to the exception constructor with an empty argument
260 * list can be used as the supplier. For example,
261 * {@code IllegalStateException::new}
262 *
263 * @param <X> Type of the exception to be thrown
264 * @param exceptionSupplier the supplying function that produces an
265 * exception to be thrown
266 * @return the value, if present
267 * @throws X if no value is present
268 * @throws NullPointerException if no value is present and the exception
269 * supplying function is {@code null}
270 */
271 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
272 if (isPresent) {
273 return value;
274 } else {
275 throw exceptionSupplier.get();
276 }
277 }
278
279 /**
280 * Indicates whether some other object is "equal to" this
281 * {@code OptionalDouble}. The other object is considered equal if:
282 * <ul>
283 * <li>it is also an {@code OptionalDouble} and;
284 * <li>both instances have no value present or;
285 * <li>the present values are "equal to" each other via
286 * {@code Double.compare() == 0}.
287 * </ul>
288 *
289 * @param obj an object to be tested for equality
290 * @return {@code true} if the other object is "equal to" this object
291 * otherwise {@code false}
292 */
293 @Override
294 public boolean equals(Object obj) {
295 if (this == obj) {
296 return true;
297 }
298
299 return obj instanceof OptionalDouble other
300 && (isPresent && other.isPresent
301 ? Double.compare(value, other.value) == 0
302 : isPresent == other.isPresent);
303 }
304
305 /**
306 * Returns the hash code of the value, if present, otherwise {@code 0}
307 * (zero) if no value is present.
308 *
309 * @return hash code value of the present value or {@code 0} if no value is
310 * present
311 */
312 @Override
313 public int hashCode() {
314 return isPresent ? Double.hashCode(value) : 0;
315 }
316
317 /**
318 * Returns a non-empty string representation of this {@code OptionalDouble}
319 * suitable for debugging. The exact presentation format is unspecified and
320 * may vary between implementations and versions.
321 *
322 * @implSpec
323 * If a value is present the result must include its string representation
324 * in the result. Empty and present {@code OptionalDouble}s must be
325 * unambiguously differentiable.
326 *
327 * @return the string representation of this instance
328 */
329 @Override
330 public String toString() {
331 return isPresent
332 ? ("OptionalDouble[" + value + "]")
333 : "OptionalDouble.empty";
334 }
335 }