OptionalDouble.java revision 7c6843e605b6224539b84a2d57a657668739295f 
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
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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).
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24 */
25package java.util;
26
27import java.util.function.DoubleConsumer;
28import java.util.function.DoubleSupplier;
29import java.util.function.Supplier;
30
31// Android-changed: removed ValueBased paragraph.
32/**
33 * A container object which may or may not contain a {@code double} value.
34 * If a value is present, {@code isPresent()} will return {@code true} and
35 * {@code getAsDouble()} will return 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 * (return a default value if value not present) and
40 * {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()} (execute a block
41 * of code if the value is present).
42 *
43 * @since 1.8
44 */
45public final class OptionalDouble {
46    /**
47     * Common instance for {@code empty()}.
48     */
49    private static final OptionalDouble EMPTY = new OptionalDouble();
50
51    /**
52     * If true then the value is present, otherwise indicates no value is present
53     */
54    private final boolean isPresent;
55    private final double value;
56
57    /**
58     * Construct an empty instance.
59     *
60     * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY},
61     * should exist per VM.
62     */
63    private OptionalDouble() {
64        this.isPresent = false;
65        this.value = Double.NaN;
66    }
67
68    /**
69     * Returns an empty {@code OptionalDouble} instance.  No value is present for this
70     * OptionalDouble.
71     *
72     * @apiNote Though it may be tempting to do so, avoid testing if an object
73     * is empty by comparing with {@code ==} against instances returned by
74     * {@code Option.empty()}. There is no guarantee that it is a singleton.
75     * Instead, use {@link #isPresent()}.
76     *
77     *  @return an empty {@code OptionalDouble}.
78     */
79    public static OptionalDouble empty() {
80        return EMPTY;
81    }
82
83    /**
84     * Construct an instance with the value present.
85     *
86     * @param value the double value to be present.
87     */
88    private OptionalDouble(double value) {
89        this.isPresent = true;
90        this.value = value;
91    }
92
93    /**
94     * Return an {@code OptionalDouble} with the specified value present.
95     *
96     * @param value the value to be present
97     * @return an {@code OptionalDouble} with the value present
98     */
99    public static OptionalDouble of(double value) {
100        return new OptionalDouble(value);
101    }
102
103    /**
104     * If a value is present in this {@code OptionalDouble}, returns the value,
105     * otherwise throws {@code NoSuchElementException}.
106     *
107     * @return the value held by this {@code OptionalDouble}
108     * @throws NoSuchElementException if there is no value present
109     *
110     * @see OptionalDouble#isPresent()
111     */
112    public double getAsDouble() {
113        if (!isPresent) {
114            throw new NoSuchElementException("No value present");
115        }
116        return value;
117    }
118
119    /**
120     * Return {@code true} if there is a value present, otherwise {@code false}.
121     *
122     * @return {@code true} if there is a value present, otherwise {@code false}
123     */
124    public boolean isPresent() {
125        return isPresent;
126    }
127
128    /**
129     * Have the specified consumer accept the value if a value is present,
130     * otherwise do nothing.
131     *
132     * @param consumer block to be executed if a value is present
133     * @throws NullPointerException if value is present and {@code consumer} is
134     * null
135     */
136    public void ifPresent(DoubleConsumer consumer) {
137        if (isPresent)
138            consumer.accept(value);
139    }
140
141    /**
142     * Return the value if present, otherwise return {@code other}.
143     *
144     * @param other the value to be returned if there is no value present
145     * @return the value, if present, otherwise {@code other}
146     */
147    public double orElse(double other) {
148        return isPresent ? value : other;
149    }
150
151    /**
152     * Return the value if present, otherwise invoke {@code other} and return
153     * the result of that invocation.
154     *
155     * @param other a {@code DoubleSupplier} whose result is returned if no value
156     * is present
157     * @return the value if present otherwise the result of {@code other.getAsDouble()}
158     * @throws NullPointerException if value is not present and {@code other} is
159     * null
160     */
161    public double orElseGet(DoubleSupplier other) {
162        return isPresent ? value : other.getAsDouble();
163    }
164
165    /**
166     * Return the contained value, if present, otherwise throw an exception
167     * to be created by the provided supplier.
168     *
169     * @apiNote A method reference to the exception constructor with an empty
170     * argument list can be used as the supplier. For example,
171     * {@code IllegalStateException::new}
172     *
173     * @param <X> Type of the exception to be thrown
174     * @param exceptionSupplier The supplier which will return the exception to
175     * be thrown
176     * @return the present value
177     * @throws X if there is no value present
178     * @throws NullPointerException if no value is present and
179     * {@code exceptionSupplier} is null
180     */
181    public<X extends Throwable> double orElseThrow(Supplier<X> exceptionSupplier) throws X {
182        if (isPresent) {
183            return value;
184        } else {
185            throw exceptionSupplier.get();
186        }
187    }
188
189    /**
190     * Indicates whether some other object is "equal to" this OptionalDouble. The
191     * other object is considered equal if:
192     * <ul>
193     * <li>it is also an {@code OptionalDouble} and;
194     * <li>both instances have no value present or;
195     * <li>the present values are "equal to" each other via {@code Double.compare() == 0}.
196     * </ul>
197     *
198     * @param obj an object to be tested for equality
199     * @return {code true} if the other object is "equal to" this object
200     * otherwise {@code false}
201     */
202    @Override
203    public boolean equals(Object obj) {
204        if (this == obj) {
205            return true;
206        }
207
208        if (!(obj instanceof OptionalDouble)) {
209            return false;
210        }
211
212        OptionalDouble other = (OptionalDouble) obj;
213        return (isPresent && other.isPresent)
214               ? Double.compare(value, other.value) == 0
215               : isPresent == other.isPresent;
216    }
217
218    /**
219     * Returns the hash code value of the present value, if any, or 0 (zero) if
220     * no value is present.
221     *
222     * @return hash code value of the present value or 0 if no value is present
223     */
224    @Override
225    public int hashCode() {
226        return isPresent ? Double.hashCode(value) : 0;
227    }
228
229    /**
230     * {@inheritDoc}
231     *
232     * Returns a non-empty string representation of this object suitable for
233     * debugging. The exact presentation format is unspecified and may vary
234     * between implementations and versions.
235     *
236     * @implSpec If a value is present the result must include its string
237     * representation in the result. Empty and present instances must be
238     * unambiguously differentiable.
239     *
240     * @return the string representation of this instance
241     */
242    @Override
243    public String toString() {
244        return isPresent
245                ? String.format("OptionalDouble[%s]", value)
246                : "OptionalDouble.empty";
247    }
248}
249