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.LongConsumer;
28 import java.util.function.LongSupplier;
29 import java.util.function.Supplier;
30
31 /**
32 * A container object which may or may not contain a {@code long} value.
33 * If a value is present, {@code isPresent()} will return {@code true} and
34 * {@code getAsLong()} 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(long) orElse()}
38 * (return a default value if value not present) and
39 * {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (execute a block
40 * of code if the value is present).
41 *
42 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
43 * class; use of identity-sensitive operations (including reference equality
44 * ({@code ==}), identity hash code, or synchronization) on instances of
45 * {@code OptionalLong} may have unpredictable effects and should be avoided.
46 *
47 * @since 1.8
48 */
49 public final class OptionalLong {
50 /**
51 * Common instance for {@code empty()}.
52 */
53 private static final OptionalLong EMPTY = new OptionalLong();
54
55 /**
56 * If true then the value is present, otherwise indicates no value is present
57 */
58 private final boolean isPresent;
59 private final long value;
60
61 /**
62 * Construct an empty instance.
63 *
64 * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
65 * should exist per VM.
66 */
67 private OptionalLong() {
68 this.isPresent = false;
69 this.value = 0;
70 }
71
72 /**
73 * Returns an empty {@code OptionalLong} instance. No value is present for this
74 * OptionalLong.
75 *
76 * @apiNote Though it may be tempting to do so, avoid testing if an object
77 * is empty by comparing with {@code ==} against instances returned by
78 * {@code Option.empty()}. There is no guarantee that it is a singleton.
79 * Instead, use {@link #isPresent()}.
80 *
81 * @return an empty {@code OptionalLong}.
82 */
83 public static OptionalLong empty() {
84 return EMPTY;
85 }
86
87 /**
88 * Construct an instance with the value present.
89 *
90 * @param value the long value to be present
91 */
92 private OptionalLong(long value) {
93 this.isPresent = true;
94 this.value = value;
95 }
96
97 /**
98 * Return an {@code OptionalLong} with the specified value present.
99 *
100 * @param value the value to be present
101 * @return an {@code OptionalLong} with the value present
102 */
103 public static OptionalLong of(long value) {
104 return new OptionalLong(value);
105 }
106
107 /**
108 * If a value is present in this {@code OptionalLong}, returns the value,
109 * otherwise throws {@code NoSuchElementException}.
110 *
111 * @return the value held by this {@code OptionalLong}
112 * @throws NoSuchElementException if there is no value present
113 *
114 * @see OptionalLong#isPresent()
115 */
116 public long getAsLong() {
117 if (!isPresent) {
118 throw new NoSuchElementException("No value present");
119 }
120 return value;
121 }
122
123 /**
124 * Return {@code true} if there is a value present, otherwise {@code false}.
125 *
126 * @return {@code true} if there is a value present, otherwise {@code false}
127 */
128 public boolean isPresent() {
129 return isPresent;
130 }
131
132 /**
133 * Have the specified consumer accept the value if a value is present,
134 * otherwise do nothing.
135 *
136 * @param consumer block to be executed if a value is present
137 * @throws NullPointerException if value is present and {@code consumer} is
138 * null
139 */
140 public void ifPresent(LongConsumer consumer) {
141 if (isPresent)
142 consumer.accept(value);
143 }
144
145 /**
146 * Return the value if present, otherwise return {@code other}.
147 *
148 * @param other the value to be returned if there is no value present
149 * @return the value, if present, otherwise {@code other}
150 */
151 public long orElse(long other) {
152 return isPresent ? value : other;
153 }
154
155 /**
156 * Return the value if present, otherwise invoke {@code other} and return
157 * the result of that invocation.
158 *
159 * @param other a {@code LongSupplier} whose result is returned if no value
160 * is present
161 * @return the value if present otherwise the result of {@code other.getAsLong()}
162 * @throws NullPointerException if value is not present and {@code other} is
163 * null
164 */
165 public long orElseGet(LongSupplier other) {
166 return isPresent ? value : other.getAsLong();
167 }
168
169 /**
170 * Return the contained value, if present, otherwise throw an exception
171 * to be created by the provided supplier.
172 *
173 * @apiNote A method reference to the exception constructor with an empty
174 * argument list can be used as the supplier. For example,
175 * {@code IllegalStateException::new}
176 *
177 * @param <X> Type of the exception to be thrown
178 * @param exceptionSupplier The supplier which will return the exception to
179 * be thrown
180 * @return the present value
181 * @throws X if there is no value present
182 * @throws NullPointerException if no value is present and
183 * {@code exceptionSupplier} is null
184 */
185 public<X extends Throwable> long orElseThrow(Supplier<X> exceptionSupplier) throws X {
186 if (isPresent) {
187 return value;
188 } else {
189 throw exceptionSupplier.get();
190 }
191 }
192
193 /**
194 * Indicates whether some other object is "equal to" this OptionalLong. The
195 * other object is considered equal if:
196 * <ul>
197 * <li>it is also an {@code OptionalLong} and;
198 * <li>both instances have no value present or;
199 * <li>the present values are "equal to" each other via {@code ==}.
200 * </ul>
201 *
202 * @param obj an object to be tested for equality
203 * @return {code true} if the other object is "equal to" this object
204 * otherwise {@code false}
205 */
206 @Override
207 public boolean equals(Object obj) {
208 if (this == obj) {
209 return true;
210 }
211
212 if (!(obj instanceof OptionalLong)) {
213 return false;
214 }
215
216 OptionalLong other = (OptionalLong) obj;
217 return (isPresent && other.isPresent)
218 ? value == other.value
219 : isPresent == other.isPresent;
220 }
221
222 /**
223 * Returns the hash code value of the present value, if any, or 0 (zero) if
224 * no value is present.
225 *
226 * @return hash code value of the present value or 0 if no value is present
227 */
228 @Override
229 public int hashCode() {
230 return isPresent ? Long.hashCode(value) : 0;
231 }
232
233 /**
234 * {@inheritDoc}
235 *
236 * Returns a non-empty string representation of this object suitable for
237 * debugging. The exact presentation format is unspecified and may vary
238 * between implementations and versions.
239 *
240 * @implSpec If a value is present the result must include its string
241 * representation in the result. Empty and present instances must be
242 * unambiguously differentiable.
243 *
244 * @return the string representation of this instance
245 */
246 @Override
247 public String toString() {
248 return isPresent
249 ? String.format("OptionalLong[%s]", value)
250 : "OptionalLong.empty";
251 }
252 }