1 /*
2 * Copyright (c) 2012, 2013, 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
31 /**
32 * A container object which may or may not contain a {@code double} value.
33 * If a value is present, {@code isPresent()} will return {@code true} and
34 * {@code get()} will return the value.
35 *
36 * <p>Additional methods that depend on the presence or absence of a contained
37 * value are provided, such as {@link #orElse(double) orElse()}
38 * (return a default value if value not present) and
39 * {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()} (execute a block
40 * of code if the value is present).
41 *
42 * @since 1.8
43 */
44 public final class OptionalDouble {
45 /**
46 * Common instance for {@code empty()}.
47 */
48 private static final OptionalDouble EMPTY = new OptionalDouble();
49
50 /**
51 * If true then the value is present, otherwise indicates no value is present
52 */
53 private final boolean isPresent;
54 private final double value;
55
56 /**
57 * Construct an empty instance.
58 *
59 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
60 * should exist per VM.
61 */
62 private OptionalDouble() {
63 this.isPresent = false;
64 this.value = Double.NaN;
65 }
66
67 /**
68 * Returns an empty {@code OptionalDouble} instance. No value is present for this
69 * OptionalDouble.
70 *
71 * @apiNote Though it may be tempting to do so, avoid testing if an object
72 * is empty by comparing with {@code ==} against instances returned by
73 * {@code Option.empty()}. There is no guarantee that it is a singleton.
74 * Instead, use {@link #isPresent()}.
75 *
76 * @return an empty {@code OptionalDouble}.
77 */
78 public static OptionalDouble empty() {
79 return EMPTY;
80 }
81
82 /**
83 * Construct an instance with the value present.
84 *
85 * @param value the double value to be present.
86 */
87 private OptionalDouble(double value) {
88 this.isPresent = true;
89 this.value = value;
90 }
91
92 /**
93 * Return an {@code OptionalDouble} with the specified value present.
94 *
95 * @param value the value to be present
96 * @return an {@code OptionalDouble} with the value present
97 */
98 public static OptionalDouble of(double value) {
99 return new OptionalDouble(value);
100 }
101
102 /**
103 * If a value is present in this {@code OptionalDouble}, returns the value,
104 * otherwise throws {@code NoSuchElementException}.
105 *
106 * @return the value held by this {@code OptionalDouble}
107 * @throws NoSuchElementException if there is no value present
108 *
109 * @see OptionalDouble#isPresent()
110 */
111 public double getAsDouble() {
112 if (!isPresent) {
113 throw new NoSuchElementException("No value present");
114 }
115 return value;
116 }
117
118 /**
119 * Return {@code true} if there is a value present, otherwise {@code false}.
120 *
121 * @return {@code true} if there is a value present, otherwise {@code false}
122 */
123 public boolean isPresent() {
124 return isPresent;
125 }
126
127 /**
128 * Have the specified consumer accept the value if a value is present,
129 * otherwise do nothing.
130 *
131 * @param consumer block to be executed if a value is present
132 * @throws NullPointerException if value is present and {@code consumer} is
133 * null
134 */
135 public void ifPresent(DoubleConsumer consumer) {
136 if (isPresent)
137 consumer.accept(value);
138 }
139
140 /**
141 * Return the value if present, otherwise return {@code other}.
142 *
143 * @param other the value to be returned if there is no value present
144 * @return the value, if present, otherwise {@code other}
145 */
146 public double orElse(double other) {
147 return isPresent ? value : other;
148 }
149
150 /**
151 * Return the value if present, otherwise invoke {@code other} and return
152 * the result of that invocation.
153 *
154 * @param other a {@code DoubleSupplier} whose result is returned if no value
155 * is present
156 * @return the value if present otherwise the result of {@code other.getAsDouble()}
157 * @throws NullPointerException if value is not present and {@code other} is
158 * null
159 */
160 public double orElseGet(DoubleSupplier other) {
161 return isPresent ? value : other.getAsDouble();
162 }
163
164 /**
165 * Return the contained value, if present, otherwise throw an exception
166 * to be created by the provided supplier.
167 *
168 * @apiNote A method reference to the exception constructor with an empty
169 * argument list can be used as the supplier. For example,
170 * {@code IllegalStateException::new}
171 *
172 * @param <X> Type of the exception to be thrown
173 * @param exceptionSupplier The supplier which will return the exception to
174 * be thrown
175 * @return the present value
176 * @throws X if there is no value present
177 * @throws NullPointerException if no value is present and
178 * {@code exceptionSupplier} is null
179 */
180 public<X extends Throwable> double orElseThrow(Supplier<X> exceptionSupplier) throws X {
181 if (isPresent) {
182 return value;
183 } else {
184 throw exceptionSupplier.get();
185 }
186 }
187
188 /**
189 * Indicates whether some other object is "equal to" this Optional. The
190 * other object is considered equal if:
191 * <ul>
192 * <li>it is also an {@code OptionalInt} and;
193 * <li>both instances have no value present or;
194 * <li>the present values are "equal to" each other via {@code Double.compare() == 0}.
195 * </ul>
196 *
197 * @param obj an object to be tested for equality
198 * @return {code true} if the other object is "equal to" this object
199 * otherwise {@code false}
200 */
201 @Override
202 public boolean equals(Object obj) {
203 if (this == obj) {
204 return true;
205 }
206
207 if (!(obj instanceof OptionalDouble)) {
208 return false;
209 }
210
211 OptionalDouble other = (OptionalDouble) obj;
212 return (isPresent && other.isPresent)
213 ? Double.compare(value, other.value) == 0
214 : isPresent == other.isPresent;
215 }
216
217 /**
218 * Returns the hash code value of the present value, if any, or 0 (zero) if
219 * no value is present.
220 *
221 * @return hash code value of the present value or 0 if no value is present
222 */
223 @Override
224 public int hashCode() {
225 return isPresent ? Double.hashCode(value) : 0;
226 }
227
228 /**
229 * Returns a non-empty string representation of this OptionalDouble suitable for
230 * debugging. The exact presentation format is unspecified and may vary
231 * between implementations and versions.
232 *
233 * @implSpec If a value is present the result must include its string
234 * representation in the result. Empty and present OptionalDoubless must be
235 * unambiguously differentiable.
236 *
237 * @return the string representation of this instance
238 */
239 @Override
240 public String toString() {
241 return isPresent
242 ? String.format("OptionalDouble[%s]", value)
243 : "OptionalDouble.empty";
244 }
245 }