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(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." A variable whose type is
51 * {@code OptionalDouble} should never itself be {@code null}; it should always point
52 * to an {@code OptionalDouble} instance.
53 *
54 * @since 1.8
55 */
56 public final class OptionalDouble {
57 /**
58 * Common instance for {@code empty()}.
59 */
60 private static final OptionalDouble EMPTY = new OptionalDouble();
61
62 /**
63 * If true then the value is present, otherwise indicates no value is present
64 */
65 private final boolean isPresent;
66 private final double value;
67
68 /**
69 * Construct an empty instance.
70 *
71 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
72 * should exist per VM.
73 */
74 private OptionalDouble() {
75 this.isPresent = false;
76 this.value = Double.NaN;
77 }
78
79 /**
80 * Returns an empty {@code OptionalDouble} instance. No value is present
81 * for this {@code OptionalDouble}.
82 *
83 * @apiNote
84 * Though it may be tempting to do so, avoid testing if an object is empty
85 * by comparing with {@code ==} against instances returned by
86 * {@code OptionalDouble.empty()}. There is no guarantee that it is a singleton.
87 * Instead, use {@link #isPresent()}.
88 *
89 * @return an empty {@code OptionalDouble}.
90 */
91 public static OptionalDouble empty() {
92 return EMPTY;
93 }
94
95 /**
96 * Construct an instance with the described value.
97 *
98 * @param value the double value to describe.
99 */
100 private OptionalDouble(double value) {
101 this.isPresent = true;
102 this.value = value;
103 }
104
105 /**
106 * Returns an {@code OptionalDouble} describing the given value.
107 *
108 * @param value the value to describe
109 * @return an {@code OptionalDouble} with the value present
110 */
111 public static OptionalDouble of(double value) {
112 return new OptionalDouble(value);
113 }
114
115 /**
116 * If a value is present, returns the value, otherwise throws
117 * {@code NoSuchElementException}.
118 *
119 * @apiNote
120 * The methods {@link #orElse(double) orElse} and
121 * {@link #orElseGet(DoubleSupplier) orElseGet}
122 * are generally preferable to this method, as they return a substitute
123 * value if the value is absent, instead of throwing an exception.
124 *
125 * @return the value described by this {@code OptionalDouble}
126 * @throws NoSuchElementException if no value is present
127 * @see OptionalDouble#isPresent()
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 present, performs the given action with the value,
147 * otherwise does nothing.
148 *
149 * @param action the action to be performed, if a value is present
150 * @throws NullPointerException if value is present and the given action is
151 * {@code null}
152 */
153 public void ifPresent(DoubleConsumer action) {
154 if (isPresent) {
155 action.accept(value);
156 }
157 }
158
159 /**
160 * If a value is present, performs the given action with the value,
161 * otherwise performs the given empty-based action.
162 *
163 * @param action the action to be performed, if a value is present
164 * @param emptyAction the empty-based action to be performed, if no value is
165 * present
166 * @throws NullPointerException if a value is present and the given action
167 * is {@code null}, or no value is present and the given empty-based
168 * action is {@code null}.
169 * @since 9
170 */
171 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
172 if (isPresent) {
173 action.accept(value);
174 } else {
175 emptyAction.run();
176 }
177 }
178
179 /**
180 * If a value is present, returns a sequential {@link DoubleStream}
181 * containing only that value, otherwise returns an empty
182 * {@code DoubleStream}.
183 *
184 * @apiNote
185 * This method can be used to transform a {@code Stream} of optional doubles
186 * to a {@code DoubleStream} of present doubles:
187 * <pre>{@code
188 * Stream<OptionalDouble> os = ..
189 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
190 * }</pre>
191 *
192 * @return the optional value as a {@code DoubleStream}
193 * @since 9
194 */
195 public DoubleStream stream() {
196 if (isPresent) {
197 return DoubleStream.of(value);
198 } else {
199 return DoubleStream.empty();
200 }
201 }
202
203 /**
204 * If a value is present, returns the value, otherwise returns
205 * {@code other}.
206 *
207 * @param other the value to be returned, if no value is present
208 * @return the value, if present, otherwise {@code other}
209 */
210 public double orElse(double other) {
211 return isPresent ? value : other;
212 }
213
214 /**
215 * If a value is present, returns the value, otherwise returns the result
216 * produced by the supplying function.
217 *
218 * @param supplier the supplying function that produces a value to be returned
219 * @return the value, if present, otherwise the result produced by the
220 * supplying function
221 * @throws NullPointerException if no value is present and the supplying
222 * function is {@code null}
223 */
224 public double orElseGet(DoubleSupplier supplier) {
225 return isPresent ? value : supplier.getAsDouble();
226 }
227
228 /**
229 * If a value is present, returns the value, otherwise throws an exception
230 * produced by the exception supplying function.
231 *
232 * @apiNote
233 * A method reference to the exception constructor with an empty argument
234 * list can be used as the supplier. For example,
235 * {@code IllegalStateException::new}
236 *
237 * @param <X> Type of the exception to be thrown
238 * @param exceptionSupplier the supplying function that produces an
239 * exception to be thrown
240 * @return the value, if present
241 * @throws X if no value is present
242 * @throws NullPointerException if no value is present and the exception
243 * supplying function is {@code null}
244 */
245 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
246 if (isPresent) {
247 return value;
248 } else {
249 throw exceptionSupplier.get();
250 }
251 }
252
253 /**
254 * Indicates whether some other object is "equal to" this
255 * {@code OptionalDouble}. The other object is considered equal if:
256 * <ul>
257 * <li>it is also an {@code OptionalDouble} and;
258 * <li>both instances have no value present or;
259 * <li>the present values are "equal to" each other via
260 * {@code Double.compare() == 0}.
261 * </ul>
262 *
263 * @param obj an object to be tested for equality
264 * @return {@code true} if the other object is "equal to" this object
265 * otherwise {@code false}
266 */
267 @Override
268 public boolean equals(Object obj) {
269 if (this == obj) {
270 return true;
271 }
272
273 if (!(obj instanceof OptionalDouble)) {
274 return false;
275 }
276
277 OptionalDouble other = (OptionalDouble) obj;
278 return (isPresent && other.isPresent)
279 ? Double.compare(value, other.value) == 0
280 : isPresent == other.isPresent;
281 }
282
283 /**
284 * Returns the hash code of the value, if present, otherwise {@code 0}
285 * (zero) if no value is present.
286 *
287 * @return hash code value of the present value or {@code 0} if no value is
288 * present
289 */
290 @Override
291 public int hashCode() {
292 return isPresent ? Double.hashCode(value) : 0;
293 }
294
295 /**
296 * Returns a non-empty string representation of this {@code OptionalDouble}
297 * suitable for debugging. The exact presentation format is unspecified and
298 * may vary between implementations and versions.
299 *
300 * @implSpec
301 * If a value is present the result must include its string representation
302 * in the result. Empty and present {@code OptionalDouble}s must be
303 * unambiguously differentiable.
304 *
305 * @return the string representation of this instance
306 */
307 @Override
308 public String toString() {
309 return isPresent
310 ? String.format("OptionalDouble[%s]", value)
311 : "OptionalDouble.empty";
312 }
313 }