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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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 public final class OptionalDouble {
60 /**
61 * Common instance for {@code empty()}.
62 */
63 private static final OptionalDouble EMPTY = new OptionalDouble();
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 double value;
70
71 /**
72 * Construct an empty instance.
73 *
74 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
75 * should exist per VM.
76 */
77 private OptionalDouble() {
78 this.isPresent = false;
79 this.value = Double.NaN;
80 }
81
82 /**
83 * Returns an empty {@code OptionalDouble} instance. No value is present
84 * for this {@code OptionalDouble}.
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 OptionalDouble.empty()}. There is no guarantee that it is a singleton.
90 * Instead, use {@link #isEmpty()} or {@link #isPresent()}.
91 *
92 * @return an empty {@code OptionalDouble}.
93 */
94 public static OptionalDouble empty() {
95 return EMPTY;
96 }
97
98 /**
99 * Construct an instance with the described value.
100 *
101 * @param value the double value to describe.
102 */
103 private OptionalDouble(double value) {
104 this.isPresent = true;
105 this.value = value;
106 }
107
108 /**
109 * Returns an {@code OptionalDouble} describing the given value.
110 *
111 * @param value the value to describe
112 * @return an {@code OptionalDouble} with the value present
113 */
114 public static OptionalDouble of(double value) {
115 return new OptionalDouble(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 OptionalDouble}
126 * @throws NoSuchElementException if no value is present
127 */
128 public double getAsDouble() {
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(DoubleConsumer 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(DoubleConsumer 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 DoubleStream}
191 * containing only that value, otherwise returns an empty
192 * {@code DoubleStream}.
193 *
194 * @apiNote
195 * This method can be used to transform a {@code Stream} of optional doubles
196 * to a {@code DoubleStream} of present doubles:
197 * <pre>{@code
198 * Stream<OptionalDouble> os = ..
199 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
200 * }</pre>
201 *
202 * @return the optional value as a {@code DoubleStream}
203 * @since 9
204 */
205 public DoubleStream stream() {
206 if (isPresent) {
207 return DoubleStream.of(value);
208 } else {
209 return DoubleStream.empty();
210 }
211 }
212
213 /**
214 * If a value is present, returns the value, otherwise returns
215 * {@code other}.
216 *
217 * @param other the value to be returned, if no value is present
218 * @return the value, if present, otherwise {@code other}
219 */
220 public double orElse(double other) {
221 return isPresent ? value : other;
222 }
223
224 /**
225 * If a value is present, returns the value, otherwise returns the result
226 * produced by the supplying function.
227 *
228 * @param supplier the supplying function that produces a value to be returned
229 * @return the value, if present, otherwise the result produced by the
230 * supplying function
231 * @throws NullPointerException if no value is present and the supplying
232 * function is {@code null}
233 */
234 public double orElseGet(DoubleSupplier supplier) {
235 return isPresent ? value : supplier.getAsDouble();
236 }
237
238 /**
239 * If a value is present, returns the value, otherwise throws
240 * {@code NoSuchElementException}.
241 *
242 * @return the value described by this {@code OptionalDouble}
243 * @throws NoSuchElementException if no value is present
244 * @since 10
245 */
246 public double orElseThrow() {
247 if (!isPresent) {
248 throw new NoSuchElementException("No value present");
249 }
250 return value;
251 }
252
253 /**
254 * If a value is present, returns the value, otherwise throws an exception
255 * produced by the exception supplying function.
256 *
257 * @apiNote
258 * A method reference to the exception constructor with an empty argument
259 * list can be used as the supplier. For example,
260 * {@code IllegalStateException::new}
261 *
262 * @param <X> Type of the exception to be thrown
263 * @param exceptionSupplier the supplying function that produces an
264 * exception to be thrown
265 * @return the value, if present
266 * @throws X if no value is present
267 * @throws NullPointerException if no value is present and the exception
268 * supplying function is {@code null}
269 */
270 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
271 if (isPresent) {
272 return value;
273 } else {
274 throw exceptionSupplier.get();
275 }
276 }
277
278 /**
279 * Indicates whether some other object is "equal to" this
280 * {@code OptionalDouble}. The other object is considered equal if:
281 * <ul>
282 * <li>it is also an {@code OptionalDouble} and;
283 * <li>both instances have no value present or;
284 * <li>the present values are "equal to" each other via
285 * {@code Double.compare() == 0}.
286 * </ul>
287 *
288 * @param obj an object to be tested for equality
289 * @return {@code true} if the other object is "equal to" this object
290 * otherwise {@code false}
291 */
292 @Override
293 public boolean equals(Object obj) {
294 if (this == obj) {
295 return true;
296 }
297
298 return obj instanceof OptionalDouble other
299 && (isPresent && other.isPresent
300 ? Double.compare(value, other.value) == 0
301 : isPresent == other.isPresent);
302 }
303
304 /**
305 * Returns the hash code of the value, if present, otherwise {@code 0}
306 * (zero) if no value is present.
307 *
308 * @return hash code value of the present value or {@code 0} if no value is
309 * present
310 */
311 @Override
312 public int hashCode() {
313 return isPresent ? Double.hashCode(value) : 0;
314 }
315
316 /**
317 * Returns a non-empty string representation of this {@code OptionalDouble}
318 * suitable for debugging. The exact presentation format is unspecified and
319 * may vary between implementations and versions.
320 *
321 * @implSpec
322 * If a value is present the result must include its string representation
323 * in the result. Empty and present {@code OptionalDouble}s must be
324 * unambiguously differentiable.
325 *
326 * @return the string representation of this instance
327 */
328 @Override
329 public String toString() {
330 return isPresent
331 ? ("OptionalDouble[" + value + "]")
332 : "OptionalDouble.empty";
333 }
334 }