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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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(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 * @return the value described by this {@code OptionalDouble}
114 * @throws NoSuchElementException if no value is present
115 * @see OptionalDouble#isPresent()
116 */
117 public double getAsDouble() {
118 if (!isPresent) {
119 throw new NoSuchElementException("No value present");
120 }
121 return value;
122 }
123
124 /**
125 * If a value is present, returns {@code true}, otherwise {@code false}.
126 *
127 * @return {@code true} if a value is present, otherwise {@code false}
128 */
129 public boolean isPresent() {
130 return isPresent;
131 }
132
133 /**
134 * If a value is present, performs the given action with the value,
135 * otherwise does nothing.
136 *
137 * @param action the action to be performed, if a value is present
138 * @throws NullPointerException if value is present and the given action is
139 * {@code null}
140 */
141 public void ifPresent(DoubleConsumer action) {
142 if (isPresent) {
143 action.accept(value);
144 }
145 }
146
147 /**
148 * If a value is present, performs the given action with the value,
149 * otherwise performs the given empty-based action.
150 *
151 * @param action the action to be performed, if a value is present
152 * @param emptyAction the empty-based action to be performed, if no value is
153 * present
154 * @throws NullPointerException if a value is present and the given action
155 * is {@code null}, or no value is present and the given empty-based
156 * action is {@code null}.
157 * @since 9
158 */
159 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
160 if (isPresent) {
161 action.accept(value);
162 } else {
163 emptyAction.run();
164 }
165 }
166
167 /**
168 * If a value is present, returns a sequential {@link DoubleStream}
169 * containing only that value, otherwise returns an empty
170 * {@code DoubleStream}.
171 *
172 * @apiNote
173 * This method can be used to transform a {@code Stream} of optional doubles
174 * to a {@code DoubleStream} of present doubles:
175 * <pre>{@code
176 * Stream<OptionalDouble> os = ..
177 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
178 * }</pre>
179 *
180 * @return the optional value as a {@code DoubleStream}
181 * @since 9
182 */
183 public DoubleStream stream() {
184 if (isPresent) {
185 return DoubleStream.of(value);
186 } else {
187 return DoubleStream.empty();
188 }
189 }
190
191 /**
192 * If a value is present, returns the value, otherwise returns
193 * {@code other}.
194 *
195 * @param other the value to be returned, if no value is present
196 * @return the value, if present, otherwise {@code other}
197 */
198 public double orElse(double other) {
199 return isPresent ? value : other;
200 }
201
202 /**
203 * If a value is present, returns the value, otherwise returns the result
204 * produced by the supplying function.
205 *
206 * @param supplier the supplying function that produces a value to be returned
207 * @return the value, if present, otherwise the result produced by the
208 * supplying function
209 * @throws NullPointerException if no value is present and the supplying
210 * function is {@code null}
211 */
212 public double orElseGet(DoubleSupplier supplier) {
213 return isPresent ? value : supplier.getAsDouble();
214 }
215
216 /**
217 * If a value is present, returns the value, otherwise throws an exception
218 * produced by the exception supplying function.
219 *
220 * @apiNote
221 * A method reference to the exception constructor with an empty argument
222 * list can be used as the supplier. For example,
223 * {@code IllegalStateException::new}
224 *
225 * @param <X> Type of the exception to be thrown
226 * @param exceptionSupplier the supplying function that produces an
227 * exception to be thrown
228 * @return the value, if present
229 * @throws X if no value is present
230 * @throws NullPointerException if no value is present and the exception
231 * supplying function is {@code null}
232 */
233 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
234 if (isPresent) {
235 return value;
236 } else {
237 throw exceptionSupplier.get();
238 }
239 }
240
241 /**
242 * Indicates whether some other object is "equal to" this
243 * {@code OptionalDouble}. The other object is considered equal if:
244 * <ul>
245 * <li>it is also an {@code OptionalDouble} and;
246 * <li>both instances have no value present or;
247 * <li>the present values are "equal to" each other via
248 * {@code Double.compare() == 0}.
249 * </ul>
250 *
251 * @param obj an object to be tested for equality
252 * @return {@code true} if the other object is "equal to" this object
253 * otherwise {@code false}
254 */
255 @Override
256 public boolean equals(Object obj) {
257 if (this == obj) {
258 return true;
259 }
260
261 if (!(obj instanceof OptionalDouble)) {
262 return false;
263 }
264
265 OptionalDouble other = (OptionalDouble) obj;
266 return (isPresent && other.isPresent)
267 ? Double.compare(value, other.value) == 0
268 : isPresent == other.isPresent;
269 }
270
271 /**
272 * Returns the hash code of the value, if present, otherwise {@code 0}
273 * (zero) if no value is present.
274 *
275 * @return hash code value of the present value or {@code 0} if no value is
276 * present
277 */
278 @Override
279 public int hashCode() {
280 return isPresent ? Double.hashCode(value) : 0;
281 }
282
283 /**
284 * Returns a non-empty string representation of this {@code OptionalDouble}
285 * suitable for debugging. The exact presentation format is unspecified and
286 * may vary between implementations and versions.
287 *
288 * @implSpec
289 * If a value is present the result must include its string representation
290 * in the result. Empty and present {@code OptionalDouble}s must be
291 * unambiguously differentiable.
292 *
293 * @return the string representation of this instance
294 */
295 @Override
296 public String toString() {
297 return isPresent
298 ? String.format("OptionalDouble[%s]", value)
299 : "OptionalDouble.empty";
300 }
301 }