1 /*
2 * Copyright (c) 2012, 2017, 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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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. If a
34 * value is present, {@code isPresent()} returns {@code true} and
35 * {@code getAsDouble()} returns the value.
36 *
37 * <p>Additional methods that depend on the presence or absence of a contained
38 * value are provided, such as {@link #orElse(double) orElse()}
39 * (returns a default value if no value is present) and
40 * {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()} (performs
41 * an action if a value is present).
42 *
43 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
44 * class; use of identity-sensitive operations (including reference equality
45 * ({@code ==}), identity hash code, or synchronization) on instances of
46 * {@code OptionalDouble} may have unpredictable results and should be avoided.
47 *
48 * @apiNote
49 * {@code OptionalDouble} is primarily intended for use as a method return type where
50 * there is a clear need to represent "no result," and where using {@code null}
51 * is likely to cause errors. A variable whose type is {@code OptionalDouble} should
52 * never itself be {@code null}; it should always point to an {@code OptionalDouble}
53 * 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 methods {@link #orElse(double) orElse()} and
122 * {@link #orElseGet(java.util.function.DoubleSupplier) orElseGet()}
123 * are generally preferable to this method, as they return a substitute
124 * value if the value is absent, instead of throwing an exception.
125 *
126 * @return the value described by this {@code OptionalDouble}
127 * @throws NoSuchElementException if no value is present
128 * @see OptionalDouble#isPresent()
129 */
130 public double getAsDouble() {
131 if (!isPresent) {
132 throw new NoSuchElementException("No value present");
133 }
134 return value;
135 }
136
137 /**
138 * If a value is present, returns {@code true}, otherwise {@code false}.
139 *
140 * @return {@code true} if a value is present, otherwise {@code false}
141 */
142 public boolean isPresent() {
143 return isPresent;
144 }
145
146 /**
147 * If a value is present, performs the given action with the value,
148 * otherwise does nothing.
149 *
150 * @param action the action to be performed, if a value is present
151 * @throws NullPointerException if value is present and the given action is
152 * {@code null}
153 */
154 public void ifPresent(DoubleConsumer action) {
155 if (isPresent) {
156 action.accept(value);
157 }
158 }
159
160 /**
161 * If a value is present, performs the given action with the value,
162 * otherwise performs the given empty-based action.
163 *
164 * @param action the action to be performed, if a value is present
165 * @param emptyAction the empty-based action to be performed, if no value is
166 * present
167 * @throws NullPointerException if a value is present and the given action
168 * is {@code null}, or no value is present and the given empty-based
169 * action is {@code null}.
170 * @since 9
171 */
172 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
173 if (isPresent) {
174 action.accept(value);
175 } else {
176 emptyAction.run();
177 }
178 }
179
180 /**
181 * If a value is present, returns a sequential {@link DoubleStream}
182 * containing only that value, otherwise returns an empty
183 * {@code DoubleStream}.
184 *
185 * @apiNote
186 * This method can be used to transform a {@code Stream} of optional doubles
187 * to a {@code DoubleStream} of present doubles:
188 * <pre>{@code
189 * Stream<OptionalDouble> os = ..
190 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
191 * }</pre>
192 *
193 * @return the optional value as a {@code DoubleStream}
194 * @since 9
195 */
196 public DoubleStream stream() {
197 if (isPresent) {
198 return DoubleStream.of(value);
199 } else {
200 return DoubleStream.empty();
201 }
202 }
203
204 /**
205 * If a value is present, returns the value, otherwise returns
206 * {@code other}.
207 *
208 * @param other the value to be returned, if no value is present
209 * @return the value, if present, otherwise {@code other}
210 */
211 public double orElse(double other) {
212 return isPresent ? value : other;
213 }
214
215 /**
216 * If a value is present, returns the value, otherwise returns the result
217 * produced by the supplying function.
218 *
219 * @param supplier the supplying function that produces a value to be returned
220 * @return the value, if present, otherwise the result produced by the
221 * supplying function
222 * @throws NullPointerException if no value is present and the supplying
223 * function is {@code null}
224 */
225 public double orElseGet(DoubleSupplier supplier) {
226 return isPresent ? value : supplier.getAsDouble();
227 }
228
229 /**
230 * If a value is present, returns the value, otherwise throws an exception
231 * produced by the exception supplying function.
232 *
233 * @apiNote
234 * A method reference to the exception constructor with an empty argument
235 * list can be used as the supplier. For example,
236 * {@code IllegalStateException::new}
237 *
238 * @param <X> Type of the exception to be thrown
239 * @param exceptionSupplier the supplying function that produces an
240 * exception to be thrown
241 * @return the value, if present
242 * @throws X if no value is present
243 * @throws NullPointerException if no value is present and the exception
244 * supplying function is {@code null}
245 */
246 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
247 if (isPresent) {
248 return value;
249 } else {
250 throw exceptionSupplier.get();
251 }
252 }
253
254 /**
255 * Indicates whether some other object is "equal to" this
256 * {@code OptionalDouble}. The other object is considered equal if:
257 * <ul>
258 * <li>it is also an {@code OptionalDouble} and;
259 * <li>both instances have no value present or;
260 * <li>the present values are "equal to" each other via
261 * {@code Double.compare() == 0}.
262 * </ul>
263 *
264 * @param obj an object to be tested for equality
265 * @return {@code true} if the other object is "equal to" this object
266 * otherwise {@code false}
267 */
268 @Override
269 public boolean equals(Object obj) {
270 if (this == obj) {
271 return true;
272 }
273
274 if (!(obj instanceof OptionalDouble)) {
275 return false;
276 }
277
278 OptionalDouble other = (OptionalDouble) obj;
279 return (isPresent && other.isPresent)
280 ? Double.compare(value, other.value) == 0
281 : isPresent == other.isPresent;
282 }
283
284 /**
285 * Returns the hash code of the value, if present, otherwise {@code 0}
286 * (zero) if no value is present.
287 *
288 * @return hash code value of the present value or {@code 0} if no value is
289 * present
290 */
291 @Override
292 public int hashCode() {
293 return isPresent ? Double.hashCode(value) : 0;
294 }
295
296 /**
297 * Returns a non-empty string representation of this {@code OptionalDouble}
298 * suitable for debugging. The exact presentation format is unspecified and
299 * may vary between implementations and versions.
300 *
301 * @implSpec
302 * If a value is present the result must include its string representation
303 * in the result. Empty and present {@code OptionalDouble}s must be
304 * unambiguously differentiable.
305 *
306 * @return the string representation of this instance
307 */
308 @Override
309 public String toString() {
310 return isPresent
311 ? String.format("OptionalDouble[%s]", value)
312 : "OptionalDouble.empty";
313 }
314 }