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()} (perform an
41 * action 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 * If a value is present, perform the given action with the value,
135 * otherwise do nothing.
136 *
137 * @param action the action to be performed if a value is present
138 * @throws NullPointerException if a value is present and {@code action} is
139 * null
140 */
141 public void ifPresent(LongConsumer action) {
142 if (isPresent) {
143 action.accept(value);
144 }
145 }
146
147 /**
148 * If a value is present, perform the given action with the value,
149 * otherwise perform the given empty-based action.
150 *
151 * @param action the action to be performed if a value is present
152 * @param emptyAction the empty-based action to be performed if a value is
153 * not present
154 * @throws NullPointerException if a value is present and {@code action} is
155 * null, or a value is not present and {@code emptyAction} is null.
156 * @since 1.9
157 */
158 public void ifPresentOrElse(LongConsumer action, Runnable emptyAction) {
159 if (isPresent) {
160 action.accept(value);
161 } else {
162 emptyAction.run();
163 }
164 }
165
166 /**
167 * If a value is present return a sequential {@link LongStream} containing
168 * only that value, otherwise return an empty {@code LongStream}.
169 *
170 * @apiNote This method can be used to transform a {@code Stream} of
171 * optional longs to a {@code LongStream} of present longs:
172 *
173 * <pre>{@code
174 * Stream<OptionalLong> os = ..
175 * LongStream s = os.flatMapToLong(OptionalLong::stream)
176 * }</pre>
177 *
178 * @return the optional value as a {@code LongStream}
179 * @since 1.9
180 */
181 public LongStream stream() {
182 if (isPresent) {
183 return LongStream.of(value);
184 } else {
185 return LongStream.empty();
186 }
187 }
188
189 /**
190 * Return the value if present, otherwise return {@code other}.
191 *
192 * @param other the value to be returned if there is no value present
193 * @return the value, if present, otherwise {@code other}
194 */
195 public long orElse(long other) {
196 return isPresent ? value : other;
197 }
198
199 /**
200 * Return the value if present, otherwise invoke {@code other} and return
201 * the result of that invocation.
202 *
203 * @param other a {@code LongSupplier} whose result is returned if no value
204 * is present
205 * @return the value if present otherwise the result of {@code other.getAsLong()}
206 * @throws NullPointerException if value is not present and {@code other} is
207 * null
208 */
209 public long orElseGet(LongSupplier other) {
210 return isPresent ? value : other.getAsLong();
211 }
212
213 /**
214 * Return the contained value, if present, otherwise throw an exception
215 * to be created by the provided supplier.
216 *
217 * @apiNote A method reference to the exception constructor with an empty
218 * argument list can be used as the supplier. For example,
219 * {@code IllegalStateException::new}
220 *
221 * @param <X> Type of the exception to be thrown
222 * @param exceptionSupplier The supplier which will return the exception to
223 * be thrown
224 * @return the present value
225 * @throws X if there is no value present
226 * @throws NullPointerException if no value is present and
227 * {@code exceptionSupplier} is null
228 */
229 public<X extends Throwable> long orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
230 if (isPresent) {
231 return value;
232 } else {
233 throw exceptionSupplier.get();
234 }
235 }
236
237 /**
238 * Indicates whether some other object is "equal to" this OptionalLong. The
239 * other object is considered equal if:
240 * <ul>
241 * <li>it is also an {@code OptionalLong} and;
242 * <li>both instances have no value present or;
243 * <li>the present values are "equal to" each other via {@code ==}.
244 * </ul>
245 *
246 * @param obj an object to be tested for equality
247 * @return {code true} if the other object is "equal to" this object
248 * otherwise {@code false}
249 */
250 @Override
251 public boolean equals(Object obj) {
252 if (this == obj) {
253 return true;
254 }
255
256 if (!(obj instanceof OptionalLong)) {
257 return false;
258 }
259
260 OptionalLong other = (OptionalLong) obj;
261 return (isPresent && other.isPresent)
262 ? value == other.value
263 : isPresent == other.isPresent;
264 }
265
266 /**
267 * Returns the hash code value of the present value, if any, or 0 (zero) if
268 * no value is present.
269 *
270 * @return hash code value of the present value or 0 if no value is present
271 */
272 @Override
273 public int hashCode() {
274 return isPresent ? Long.hashCode(value) : 0;
275 }
276
277 /**
278 * {@inheritDoc}
279 *
280 * Returns a non-empty string representation of this object suitable for
281 * debugging. The exact presentation format is unspecified and may vary
282 * between implementations and versions.
283 *
284 * @implSpec If a value is present the result must include its string
285 * representation in the result. Empty and present instances must be
286 * unambiguously differentiable.
287 *
288 * @return the string representation of this instance
289 */
290 @Override
291 public String toString() {
292 return isPresent
293 ? String.format("OptionalLong[%s]", value)
294 : "OptionalLong.empty";
295 }
296 }