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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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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.
34 * If a value is present, {@code isPresent()} returns {@code true}. If no
35 * value is present, the object is considered <i>empty</i> and
36 * {@code isPresent()} returns {@code false}.
37 *
38 * <p>Additional methods that depend on the presence or absence of a contained
39 * value are provided, such as {@link #orElse(double) orElse()}
40 * (returns a default value if no value is present) and
41 * {@link #ifPresent(DoubleConsumer) ifPresent()} (performs
42 * an action if a value is present).
43 *
44 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
45 * class; use of identity-sensitive operations (including reference equality
46 * ({@code ==}), identity hash code, or synchronization) on instances of
47 * {@code OptionalDouble} may have unpredictable results and should be avoided.
48 *
49 * @apiNote
50 * {@code OptionalDouble} is primarily intended for use as a method return type where
51 * there is a clear need to represent "no result." A variable whose type is
52 * {@code OptionalDouble} should never itself be {@code null}; it should always point
53 * to an {@code OptionalDouble} 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 preferred alternative to this method is {@link #orElseThrow()}.
122 *
123 * @return the value described by this {@code OptionalDouble}
124 * @throws NoSuchElementException if no value is present
125 */
126 public double getAsDouble() {
127 if (!isPresent) {
128 throw new NoSuchElementException("No value present");
129 }
130 return value;
131 }
132
133 /**
134 * If a value is present, returns {@code true}, otherwise {@code false}.
135 *
136 * @return {@code true} if a value is present, otherwise {@code false}
137 */
138 public boolean isPresent() {
139 return isPresent;
140 }
141
142 /**
143 * If a value is present, performs the given action with the value,
144 * otherwise does nothing.
145 *
146 * @param action the action to be performed, if a value is present
147 * @throws NullPointerException if value is present and the given action is
148 * {@code null}
149 */
150 public void ifPresent(DoubleConsumer action) {
151 if (isPresent) {
152 action.accept(value);
153 }
154 }
155
156 /**
157 * If a value is present, performs the given action with the value,
158 * otherwise performs the given empty-based action.
159 *
160 * @param action the action to be performed, if a value is present
161 * @param emptyAction the empty-based action to be performed, if no value is
162 * present
163 * @throws NullPointerException if a value is present and the given action
164 * is {@code null}, or no value is present and the given empty-based
165 * action is {@code null}.
166 * @since 9
167 */
168 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) {
169 if (isPresent) {
170 action.accept(value);
171 } else {
172 emptyAction.run();
173 }
174 }
175
176 /**
177 * If a value is present, returns a sequential {@link DoubleStream}
178 * containing only that value, otherwise returns an empty
179 * {@code DoubleStream}.
180 *
181 * @apiNote
182 * This method can be used to transform a {@code Stream} of optional doubles
183 * to a {@code DoubleStream} of present doubles:
184 * <pre>{@code
185 * Stream<OptionalDouble> os = ..
186 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream)
187 * }</pre>
188 *
189 * @return the optional value as a {@code DoubleStream}
190 * @since 9
191 */
192 public DoubleStream stream() {
193 if (isPresent) {
194 return DoubleStream.of(value);
195 } else {
196 return DoubleStream.empty();
197 }
198 }
199
200 /**
201 * If a value is present, returns the value, otherwise returns
202 * {@code other}.
203 *
204 * @param other the value to be returned, if no value is present
205 * @return the value, if present, otherwise {@code other}
206 */
207 public double orElse(double other) {
208 return isPresent ? value : other;
209 }
210
211 /**
212 * If a value is present, returns the value, otherwise returns the result
213 * produced by the supplying function.
214 *
215 * @param supplier the supplying function that produces a value to be returned
216 * @return the value, if present, otherwise the result produced by the
217 * supplying function
218 * @throws NullPointerException if no value is present and the supplying
219 * function is {@code null}
220 */
221 public double orElseGet(DoubleSupplier supplier) {
222 return isPresent ? value : supplier.getAsDouble();
223 }
224
225 /**
226 * If a value is present, returns the value, otherwise throws
227 * {@code NoSuchElementException}.
228 *
229 * @return the value described by this {@code OptionalDouble}
230 * @throws NoSuchElementException if no value is present
231 * @since 10
232 */
233 public double orElseThrow() {
234 if (!isPresent) {
235 throw new NoSuchElementException("No value present");
236 }
237 return value;
238 }
239
240 /**
241 * If a value is present, returns the value, otherwise throws an exception
242 * produced by the exception supplying function.
243 *
244 * @apiNote
245 * A method reference to the exception constructor with an empty argument
246 * list can be used as the supplier. For example,
247 * {@code IllegalStateException::new}
248 *
249 * @param <X> Type of the exception to be thrown
250 * @param exceptionSupplier the supplying function that produces an
251 * exception to be thrown
252 * @return the value, if present
253 * @throws X if no value is present
254 * @throws NullPointerException if no value is present and the exception
255 * supplying function is {@code null}
256 */
257 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
258 if (isPresent) {
259 return value;
260 } else {
261 throw exceptionSupplier.get();
262 }
263 }
264
265 /**
266 * Indicates whether some other object is "equal to" this
267 * {@code OptionalDouble}. The other object is considered equal if:
268 * <ul>
269 * <li>it is also an {@code OptionalDouble} and;
270 * <li>both instances have no value present or;
271 * <li>the present values are "equal to" each other via
272 * {@code Double.compare() == 0}.
273 * </ul>
274 *
275 * @param obj an object to be tested for equality
276 * @return {@code true} if the other object is "equal to" this object
277 * otherwise {@code false}
278 */
279 @Override
280 public boolean equals(Object obj) {
281 if (this == obj) {
282 return true;
283 }
284
285 if (!(obj instanceof OptionalDouble)) {
286 return false;
287 }
288
289 OptionalDouble other = (OptionalDouble) obj;
290 return (isPresent && other.isPresent)
291 ? Double.compare(value, other.value) == 0
292 : isPresent == other.isPresent;
293 }
294
295 /**
296 * Returns the hash code of the value, if present, otherwise {@code 0}
297 * (zero) if no value is present.
298 *
299 * @return hash code value of the present value or {@code 0} if no value is
300 * present
301 */
302 @Override
303 public int hashCode() {
304 return isPresent ? Double.hashCode(value) : 0;
305 }
306
307 /**
308 * Returns a non-empty string representation of this {@code OptionalDouble}
309 * suitable for debugging. The exact presentation format is unspecified and
310 * may vary between implementations and versions.
311 *
312 * @implSpec
313 * If a value is present the result must include its string representation
314 * in the result. Empty and present {@code OptionalDouble}s must be
315 * unambiguously differentiable.
316 *
317 * @return the string representation of this instance
318 */
319 @Override
320 public String toString() {
321 return isPresent
322 ? String.format("OptionalDouble[%s]", value)
323 : "OptionalDouble.empty";
324 }
325 }