1 /*
2 * Copyright (c) 2012, 2015, 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. 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 * @since 1.8
49 */
50 public final class OptionalDouble {
51 /**
52 * Common instance for {@code empty()}.
53 */
54 private static final OptionalDouble EMPTY = new OptionalDouble();
55
56 /**
57 * If true then the value is present, otherwise indicates no value is present
58 */
59 private final boolean isPresent;
60 private final double value;
61
62 /**
63 * Construct an empty instance.
64 *
65 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
66 * should exist per VM.
67 */
68 private OptionalDouble() {
69 this.isPresent = false;
70 this.value = Double.NaN;
71 }
72
73 /**
74 * Returns an empty {@code OptionalDouble} instance. No value is present
75 * for this {@code OptionalDouble}.
76 *
77 * @apiNote
78 * Though it may be tempting to do so, avoid testing if an object is empty
79 * by comparing with {@code ==} against instances returned by
80 * {@code OptionalDouble.empty()}. There is no guarantee that it is a singleton.
81 * Instead, use {@link #isPresent()}.
82 *
83 * @return an empty {@code OptionalDouble}.
84 */
85 public static OptionalDouble empty() {
86 return EMPTY;
87 }
88
89 /**
90 * Construct an instance with the described value.
91 *
92 * @param value the double value to describe.
93 */
94 private OptionalDouble(double value) {
95 this.isPresent = true;
96 this.value = value;
97 }
98
99 /**
100 * Returns an {@code OptionalDouble} describing the given value.
101 *
102 * @param value the value to describe
103 * @return an {@code OptionalDouble} with the value present
104 */
105 public static OptionalDouble of(double value) {
106 return new OptionalDouble(value);
107 }
108
109 /**
110 * If a value is present, returns the value, otherwise throws
111 * {@code NoSuchElementException}.
112 *
113 * @deprecated
114 * This method's name {@code getAsDouble} makes it the obvious method to
115 * call to retrieve the value from this {@code OptionalDouble}. However, it has
116 * no mechanism to avoid an exception if this {@code OptionalDouble} is empty.
117 * This tends to lead to code that mishandles empty {@code OptionalDouble}
118 * values. Consider using other methods that handle the case where
119 * the {@code OptionalDouble} might be empty, such as
120 * {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()}
121 * and related methods, and
122 * {@link #orElse(double) orElse()} and related methods.
123 * Use {@link getWhenPresent()} when it is known that a value is
124 * always present.
125 *
126 * @return the value described by this {@code OptionalDouble}
127 * @throws NoSuchElementException if no value is present
128 * @see OptionalDouble#isPresent()
129 */
130 @Deprecated(since="9")
131 public double getAsDouble() {
132 if (!isPresent) {
133 throw new NoSuchElementException("No value present");
134 }
135 return value;
136 }
137
138 /**
139 * If a value is present, returns the value, otherwise throws
140 * {@code NoSuchElementException}.
141 *
142 * @apiNote
143 * Use this method only when it is known that a value is always present.
144 *
145 * @return the value described by this {@code OptionalDouble}
146 * @throws NoSuchElementException if no value is present
147 * @see OptionalDouble#isPresent()
148 */
149 public double getWhenPresent() {
150 if (!isPresent) {
151 throw new NoSuchElementException("No value present");
152 }
153 return value;
154 }
155
156 /**
157 * If a value is present, returns {@code true}, otherwise {@code false}.
158 *
159 * @return {@code true} if a value is present, otherwise {@code false}
160 */
161 public boolean isPresent() {
162 return isPresent;
163 }
164
165 /**
166 * If a value is present, performs the given action with the value,
167 * otherwise does nothing.
168 *
169 * @param action the action to be performed, if a value is present
170 * @throws NullPointerException if value is present and the given action is
171 * {@code null}
172 */
173 public void ifPresent(DoubleConsumer action) {
174 if (isPresent) {
175 action.accept(value);
176 }
177 }
178
179 /**
180 * If a value is present, performs the given action with the value,
181 * otherwise performs the given empty-based action.
182 *
183 * @param action the action to be performed, if a value is present
184 * @param emptyAction the empty-based action to be performed, if no value is
185 * present
186 * @throws NullPointerException if a value is present and the given action
187 * is {@code null}, or no value is present and the given empty-based
188 * action is {@code null}.
189 * @since 9
190 */
191 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
192 if (isPresent) {
193 action.accept(value);
194 } else {
195 emptyAction.run();
196 }
197 }
198
199 /**
200 * If a value is present, returns a sequential {@link DoubleStream}
201 * containing only that value, otherwise returns an empty
202 * {@code DoubleStream}.
203 *
204 * @apiNote
205 * This method can be used to transform a {@code Stream} of optional doubles
206 * to a {@code DoubleStream} of present doubles:
207 * <pre>{@code
208 * Stream<OptionalDouble> os = ..
209 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
210 * }</pre>
211 *
212 * @return the optional value as a {@code DoubleStream}
213 * @since 9
214 */
215 public DoubleStream stream() {
216 if (isPresent) {
217 return DoubleStream.of(value);
218 } else {
219 return DoubleStream.empty();
220 }
221 }
222
223 /**
224 * If a value is present, returns the value, otherwise returns
225 * {@code other}.
226 *
227 * @param other the value to be returned, if no value is present
228 * @return the value, if present, otherwise {@code other}
229 */
230 public double orElse(double other) {
231 return isPresent ? value : other;
232 }
233
234 /**
235 * If a value is present, returns the value, otherwise returns the result
236 * produced by the supplying function.
237 *
238 * @param supplier the supplying function that produces a value to be returned
239 * @return the value, if present, otherwise the result produced by the
240 * supplying function
241 * @throws NullPointerException if no value is present and the supplying
242 * function is {@code null}
243 */
244 public double orElseGet(DoubleSupplier supplier) {
245 return isPresent ? value : supplier.getAsDouble();
246 }
247
248 /**
249 * If a value is present, returns the value, otherwise throws an exception
250 * produced by the exception supplying function.
251 *
252 * @apiNote
253 * A method reference to the exception constructor with an empty argument
254 * list can be used as the supplier. For example,
255 * {@code IllegalStateException::new}
256 *
257 * @param <X> Type of the exception to be thrown
258 * @param exceptionSupplier the supplying function that produces an
259 * exception to be thrown
260 * @return the value, if present
261 * @throws X if no value is present
262 * @throws NullPointerException if no value is present and the exception
263 * supplying function is {@code null}
264 */
265 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
266 if (isPresent) {
267 return value;
268 } else {
269 throw exceptionSupplier.get();
270 }
271 }
272
273 /**
274 * Indicates whether some other object is "equal to" this
275 * {@code OptionalDouble}. The other object is considered equal if:
276 * <ul>
277 * <li>it is also an {@code OptionalDouble} and;
278 * <li>both instances have no value present or;
279 * <li>the present values are "equal to" each other via
280 * {@code Double.compare() == 0}.
281 * </ul>
282 *
283 * @param obj an object to be tested for equality
284 * @return {@code true} if the other object is "equal to" this object
285 * otherwise {@code false}
286 */
287 @Override
288 public boolean equals(Object obj) {
289 if (this == obj) {
290 return true;
291 }
292
293 if (!(obj instanceof OptionalDouble)) {
294 return false;
295 }
296
297 OptionalDouble other = (OptionalDouble) obj;
298 return (isPresent && other.isPresent)
299 ? Double.compare(value, other.value) == 0
300 : isPresent == other.isPresent;
301 }
302
303 /**
304 * Returns the hash code of the value, if present, otherwise {@code 0}
305 * (zero) if no value is present.
306 *
307 * @return hash code value of the present value or {@code 0} if no value is
308 * present
309 */
310 @Override
311 public int hashCode() {
312 return isPresent ? Double.hashCode(value) : 0;
313 }
314
315 /**
316 * Returns a non-empty string representation of this {@code OptionalDouble}
317 * suitable for debugging. The exact presentation format is unspecified and
318 * may vary between implementations and versions.
319 *
320 * @implSpec
321 * If a value is present the result must include its string representation
322 * in the result. Empty and present {@code OptionalDouble}s must be
323 * unambiguously differentiable.
324 *
325 * @return the string representation of this instance
326 */
327 @Override
328 public String toString() {
329 return isPresent
330 ? String.format("OptionalDouble[%s]", value)
331 : "OptionalDouble.empty";
332 }
333 }