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
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
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
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 preferred alternative to this method is {@link #orElseThrow()}.
121 *
122 * @return the value described by this {@code OptionalDouble}
123 * @throws NoSuchElementException if no value is present
124 */
125 public double getAsDouble() {
126 if (!isPresent) {
127 throw new NoSuchElementException("No value present");
128 }
129 return value;
130 }
131
132 /**
133 * If a value is present, returns {@code true}, otherwise {@code false}.
134 *
135 * @return {@code true} if a value is present, otherwise {@code false}
136 */
137 public boolean isPresent() {
138 return isPresent;
139 }
140
141 /**
142 * If a value is present, performs the given action with the value,
143 * otherwise does nothing.
144 *
145 * @param action the action to be performed, if a value is present
146 * @throws NullPointerException if value is present and the given action is
147 * {@code null}
148 */
149 public void ifPresent(DoubleConsumer action) {
150 if (isPresent) {
151 action.accept(value);
152 }
153 }
154
155 /**
156 * If a value is present, performs the given action with the value,
157 * otherwise performs the given empty-based action.
158 *
159 * @param action the action to be performed, if a value is present
160 * @param emptyAction the empty-based action to be performed, if no value is
161 * present
162 * @throws NullPointerException if a value is present and the given action
163 * is {@code null}, or no value is present and the given empty-based
164 * action is {@code null}.
165 * @since 9
166 */
167 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
168 if (isPresent) {
169 action.accept(value);
170 } else {
171 emptyAction.run();
172 }
173 }
174
175 /**
176 * If a value is present, returns a sequential {@link DoubleStream}
177 * containing only that value, otherwise returns an empty
178 * {@code DoubleStream}.
179 *
180 * @apiNote
181 * This method can be used to transform a {@code Stream} of optional doubles
182 * to a {@code DoubleStream} of present doubles:
183 * <pre>{@code
184 * Stream<OptionalDouble> os = ..
185 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
186 * }</pre>
187 *
188 * @return the optional value as a {@code DoubleStream}
189 * @since 9
190 */
191 public DoubleStream stream() {
192 if (isPresent) {
193 return DoubleStream.of(value);
194 } else {
195 return DoubleStream.empty();
196 }
197 }
198
199 /**
200 * If a value is present, returns the value, otherwise returns
201 * {@code other}.
202 *
203 * @param other the value to be returned, if no value is present
204 * @return the value, if present, otherwise {@code other}
205 */
206 public double orElse(double other) {
207 return isPresent ? value : other;
208 }
209
210 /**
211 * If a value is present, returns the value, otherwise returns the result
212 * produced by the supplying function.
213 *
214 * @param supplier the supplying function that produces a value to be returned
215 * @return the value, if present, otherwise the result produced by the
216 * supplying function
217 * @throws NullPointerException if no value is present and the supplying
218 * function is {@code null}
219 */
220 public double orElseGet(DoubleSupplier supplier) {
221 return isPresent ? value : supplier.getAsDouble();
222 }
223
224 /**
225 * If a value is present, returns the value, otherwise throws
226 * {@code NoSuchElementException}.
227 *
228 * @return the value described by this {@code OptionalDouble}
229 * @throws NoSuchElementException if no value is present
230 * @since 10
231 */
232 public double orElseThrow() {
233 if (!isPresent) {
234 throw new NoSuchElementException("No value present");
235 }
236 return value;
237 }
238
239 /**
240 * If a value is present, returns the value, otherwise throws an exception
241 * produced by the exception supplying function.
242 *
243 * @apiNote
244 * A method reference to the exception constructor with an empty argument
245 * list can be used as the supplier. For example,
246 * {@code IllegalStateException::new}
247 *
248 * @param <X> Type of the exception to be thrown
249 * @param exceptionSupplier the supplying function that produces an
250 * exception to be thrown
251 * @return the value, if present
252 * @throws X if no value is present
253 * @throws NullPointerException if no value is present and the exception
254 * supplying function is {@code null}
255 */
256 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
257 if (isPresent) {
258 return value;
259 } else {
260 throw exceptionSupplier.get();
261 }
262 }
263
264 /**
265 * Indicates whether some other object is "equal to" this
266 * {@code OptionalDouble}. The other object is considered equal if:
267 * <ul>
268 * <li>it is also an {@code OptionalDouble} and;
269 * <li>both instances have no value present or;
270 * <li>the present values are "equal to" each other via
271 * {@code Double.compare() == 0}.
272 * </ul>
273 *
274 * @param obj an object to be tested for equality
275 * @return {@code true} if the other object is "equal to" this object
276 * otherwise {@code false}
277 */
278 @Override
279 public boolean equals(Object obj) {
280 if (this == obj) {
281 return true;
282 }
283
284 if (!(obj instanceof OptionalDouble)) {
285 return false;
286 }
287
288 OptionalDouble other = (OptionalDouble) obj;
289 return (isPresent && other.isPresent)
290 ? Double.compare(value, other.value) == 0
291 : isPresent == other.isPresent;
292 }
293
294 /**
295 * Returns the hash code of the value, if present, otherwise {@code 0}
296 * (zero) if no value is present.
297 *
298 * @return hash code value of the present value or {@code 0} if no value is
299 * present
300 */
301 @Override
302 public int hashCode() {
303 return isPresent ? Double.hashCode(value) : 0;
304 }
305
306 /**
307 * Returns a non-empty string representation of this {@code OptionalDouble}
308 * suitable for debugging. The exact presentation format is unspecified and
309 * may vary between implementations and versions.
310 *
311 * @implSpec
312 * If a value is present the result must include its string representation
313 * in the result. Empty and present {@code OptionalDouble}s must be
314 * unambiguously differentiable.
315 *
316 * @return the string representation of this instance
317 */
318 @Override
319 public String toString() {
320 return isPresent
321 ? String.format("OptionalDouble[%s]", value)
322 : "OptionalDouble.empty";
323 }
324 }