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
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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="../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 OptionalDouble} may have unpredictable results and should be avoided.
48 *
49 * @apiNote
50 * {@code OptionalDouble} 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 OptionalDouble} should never itself be {@code null}; it should always point
53 * to an {@code OptionalDouble} instance.
54 *
55 * @since 1.8
56 */
57 public final class OptionalDouble {
58 /**
59 * Common instance for {@code empty()}.
60 */
61 private static final OptionalDouble EMPTY = new OptionalDouble();
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 double value;
68
69 /**
70 * Construct an empty instance.
71 *
72 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
73 * should exist per VM.
74 */
75 private OptionalDouble() {
76 this.isPresent = false;
77 this.value = Double.NaN;
78 }
79
80 /**
81 * Returns an empty {@code OptionalDouble} instance. No value is present
82 * for this {@code OptionalDouble}.
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 OptionalDouble.empty()}. There is no guarantee that it is a singleton.
88 * Instead, use {@link #isPresent()}.
89 *
90 * @return an empty {@code OptionalDouble}.
91 */
92 public static OptionalDouble empty() {
93 return EMPTY;
94 }
95
96 /**
97 * Construct an instance with the described value.
98 *
99 * @param value the double value to describe.
100 */
101 private OptionalDouble(double value) {
102 this.isPresent = true;
103 this.value = value;
104 }
105
106 /**
107 * Returns an {@code OptionalDouble} describing the given value.
108 *
109 * @param value the value to describe
110 * @return an {@code OptionalDouble} with the value present
111 */
112 public static OptionalDouble of(double value) {
113 return new OptionalDouble(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 OptionalDouble}
124 * @throws NoSuchElementException if no value is present
125 */
126 public double getAsDouble() {
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 * @since 11
148 */
149 public boolean isEmpty() {
150 return !isPresent;
151 }
152
153
154 /**
155 * If a value is present, performs the given action with the value,
156 * otherwise does nothing.
157 *
158 * @param action the action to be performed, if a value is present
159 * @throws NullPointerException if value is present and the given action is
160 * {@code null}
161 */
162 public void ifPresent(DoubleConsumer action) {
163 if (isPresent) {
164 action.accept(value);
165 }
166 }
167
168 /**
169 * If a value is present, performs the given action with the value,
170 * otherwise performs the given empty-based action.
171 *
172 * @param action the action to be performed, if a value is present
173 * @param emptyAction the empty-based action to be performed, if no value is
174 * present
175 * @throws NullPointerException if a value is present and the given action
176 * is {@code null}, or no value is present and the given empty-based
177 * action is {@code null}.
178 * @since 9
179 */
180 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
181 if (isPresent) {
182 action.accept(value);
183 } else {
184 emptyAction.run();
185 }
186 }
187
188 /**
189 * If a value is present, returns a sequential {@link DoubleStream}
190 * containing only that value, otherwise returns an empty
191 * {@code DoubleStream}.
192 *
193 * @apiNote
194 * This method can be used to transform a {@code Stream} of optional doubles
195 * to a {@code DoubleStream} of present doubles:
196 * <pre>{@code
197 * Stream<OptionalDouble> os = ..
198 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
199 * }</pre>
200 *
201 * @return the optional value as a {@code DoubleStream}
202 * @since 9
203 */
204 public DoubleStream stream() {
205 if (isPresent) {
206 return DoubleStream.of(value);
207 } else {
208 return DoubleStream.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 double orElse(double 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 double orElseGet(DoubleSupplier supplier) {
234 return isPresent ? value : supplier.getAsDouble();
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 OptionalDouble}
242 * @throws NoSuchElementException if no value is present
243 * @since 10
244 */
245 public double 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> double 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 OptionalDouble}. The other object is considered equal if:
280 * <ul>
281 * <li>it is also an {@code OptionalDouble} and;
282 * <li>both instances have no value present or;
283 * <li>the present values are "equal to" each other via
284 * {@code Double.compare() == 0}.
285 * </ul>
286 *
287 * @param obj an object to be tested for equality
288 * @return {@code true} if the other object is "equal to" this object
289 * otherwise {@code false}
290 */
291 @Override
292 public boolean equals(Object obj) {
293 if (this == obj) {
294 return true;
295 }
296
297 if (!(obj instanceof OptionalDouble)) {
298 return false;
299 }
300
301 OptionalDouble other = (OptionalDouble) obj;
302 return (isPresent && other.isPresent)
303 ? Double.compare(value, other.value) == 0
304 : isPresent == other.isPresent;
305 }
306
307 /**
308 * Returns the hash code of the value, if present, otherwise {@code 0}
309 * (zero) if no value is present.
310 *
311 * @return hash code value of the present value or {@code 0} if no value is
312 * present
313 */
314 @Override
315 public int hashCode() {
316 return isPresent ? Double.hashCode(value) : 0;
317 }
318
319 /**
320 * Returns a non-empty string representation of this {@code OptionalDouble}
321 * suitable for debugging. The exact presentation format is unspecified and
322 * may vary between implementations and versions.
323 *
324 * @implSpec
325 * If a value is present the result must include its string representation
326 * in the result. Empty and present {@code OptionalDouble}s must be
327 * unambiguously differentiable.
328 *
329 * @return the string representation of this instance
330 */
331 @Override
332 public String toString() {
333 return isPresent
334 ? String.format("OptionalDouble[%s]", value)
335 : "OptionalDouble.empty";
336 }
337 }