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
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 import java.util.stream.LongStream;
31
32 /**
33 * A container object which may or may not contain a {@code long} value.
34 * If a value is present, {@code isPresent()} will return {@code true} and
35 * {@code getAsLong()} 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(long) orElse()}
39 * (return a default value if value not present) and
40 * {@link #ifPresent(java.util.function.LongConsumer) ifPresent()} (execute a block
41 * of code if the 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 OptionalLong} may have unpredictable results and should be avoided.
47 *
48 * @since 1.8
49 */
50 public final class OptionalLong {
51 /**
52 * Common instance for {@code empty()}.
53 */
54 private static final OptionalLong EMPTY = new OptionalLong();
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 long value;
61
62 /**
63 * Construct an empty instance.
64 *
65 * @implNote generally only one empty instance, {@link OptionalLong#EMPTY},
66 * should exist per VM.
67 */
68 private OptionalLong() {
69 this.isPresent = false;
70 this.value = 0;
71 }
72
73 /**
74 * Returns an empty {@code OptionalLong} instance. No value is present for this
75 * OptionalLong.
76 *
77 * @apiNote Though it may be tempting to do so, avoid testing if an object
78 * is empty by comparing with {@code ==} against instances returned by
79 * {@code Option.empty()}. There is no guarantee that it is a singleton.
80 * Instead, use {@link #isPresent()}.
81 *
82 * @return an empty {@code OptionalLong}.
83 */
84 public static OptionalLong empty() {
85 return EMPTY;
86 }
87
88 /**
89 * Construct an instance with the value present.
90 *
91 * @param value the long value to be present
92 */
93 private OptionalLong(long value) {
94 this.isPresent = true;
95 this.value = value;
96 }
97
98 /**
99 * Return an {@code OptionalLong} with the specified value present.
100 *
101 * @param value the value to be present
102 * @return an {@code OptionalLong} with the value present
103 */
104 public static OptionalLong of(long value) {
105 return new OptionalLong(value);
106 }
107
108 /**
109 * If a value is present in this {@code OptionalLong}, returns the value,
110 * otherwise throws {@code NoSuchElementException}.
111 *
112 * @return the value held by this {@code OptionalLong}
113 * @throws NoSuchElementException if there is no value present
114 *
115 * @see OptionalLong#isPresent()
116 */
117 public long getAsLong() {
118 if (!isPresent) {
119 throw new NoSuchElementException("No value present");
120 }
121 return value;
122 }
123
124 /**
125 * Return {@code true} if there is a value present, otherwise {@code false}.
126 *
127 * @return {@code true} if there is a value present, otherwise {@code false}
128 */
129 public boolean isPresent() {
130 return isPresent;
131 }
132
133 /**
134 * Have the specified consumer accept the value if a value is present,
135 * otherwise do nothing.
136 *
137 * @param consumer block to be executed if a value is present
138 * @throws NullPointerException if value is present and {@code consumer} is
139 * null
140 */
141 public void ifPresent(LongConsumer consumer) {
142 if (isPresent) {
143 consumer.accept(value);
144 }
145 }
146
147 /**
148 * If a value is present return a sequential {@link LongStream} containing
149 * only that value, otherwise return an empty {@code LongStream}.
150 *
151 * @apiNote This method can be used to transform a {@code Stream} of
152 * optional longs to a {@code LongStream} of present longs:
153 *
154 * <pre>{@code
155 * Stream<OptionalLong> os = ..
156 * LongStream s = os.flatMapToLong(OptionalLong::stream)
157 * }</pre>
158 *
159 * @return the optional value as a {@code LongStream}
160 * @since 1.9
161 */
162 public LongStream stream() {
163 if (isPresent) {
164 return LongStream.of(value);
165 } else {
166 return LongStream.empty();
167 }
168 }
169
170 /**
171 * Return the value if present, otherwise return {@code other}.
172 *
173 * @param other the value to be returned if there is no value present
174 * @return the value, if present, otherwise {@code other}
175 */
176 public long orElse(long other) {
177 return isPresent ? value : other;
178 }
179
180 /**
181 * Return the value if present, otherwise invoke {@code other} and return
182 * the result of that invocation.
183 *
184 * @param other a {@code LongSupplier} whose result is returned if no value
185 * is present
186 * @return the value if present otherwise the result of {@code other.getAsLong()}
187 * @throws NullPointerException if value is not present and {@code other} is
188 * null
189 */
190 public long orElseGet(LongSupplier other) {
191 return isPresent ? value : other.getAsLong();
192 }
193
194 /**
195 * Return the contained value, if present, otherwise throw an exception
196 * to be created by the provided supplier.
197 *
198 * @apiNote A method reference to the exception constructor with an empty
199 * argument list can be used as the supplier. For example,
200 * {@code IllegalStateException::new}
201 *
202 * @param <X> Type of the exception to be thrown
203 * @param exceptionSupplier The supplier which will return the exception to
204 * be thrown
205 * @return the present value
206 * @throws X if there is no value present
207 * @throws NullPointerException if no value is present and
208 * {@code exceptionSupplier} is null
209 */
210 public<X extends Throwable> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
211 if (isPresent) {
212 return value;
213 } else {
214 throw exceptionSupplier.get();
215 }
216 }
217
218 /**
219 * Indicates whether some other object is "equal to" this OptionalLong. The
220 * other object is considered equal if:
221 * <ul>
222 * <li>it is also an {@code OptionalLong} and;
223 * <li>both instances have no value present or;
224 * <li>the present values are "equal to" each other via {@code ==}.
225 * </ul>
226 *
227 * @param obj an object to be tested for equality
228 * @return {code true} if the other object is "equal to" this object
229 * otherwise {@code false}
230 */
231 @Override
232 public boolean equals(Object obj) {
233 if (this == obj) {
234 return true;
235 }
236
237 if (!(obj instanceof OptionalLong)) {
238 return false;
239 }
240
241 OptionalLong other = (OptionalLong) obj;
242 return (isPresent && other.isPresent)
243 ? value == other.value
244 : isPresent == other.isPresent;
245 }
246
247 /**
248 * Returns the hash code value of the present value, if any, or 0 (zero) if
249 * no value is present.
250 *
251 * @return hash code value of the present value or 0 if no value is present
252 */
253 @Override
254 public int hashCode() {
255 return isPresent ? Long.hashCode(value) : 0;
256 }
257
258 /**
259 * {@inheritDoc}
260 *
261 * Returns a non-empty string representation of this object suitable for
262 * debugging. The exact presentation format is unspecified and may vary
263 * between implementations and versions.
264 *
265 * @implSpec If a value is present the result must include its string
266 * representation in the result. Empty and present instances must be
267 * unambiguously differentiable.
268 *
269 * @return the string representation of this instance
270 */
271 @Override
272 public String toString() {
273 return isPresent
274 ? String.format("OptionalLong[%s]", value)
275 : "OptionalLong.empty";
276 }
277 }