1 /* 2 * Copyright (c) 2012, 2020, 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.IntConsumer; 28 import java.util.function.IntSupplier; 29 import java.util.function.Supplier; 30 import java.util.stream.IntStream; 31 32 /** 33 * A container object which may or may not contain an {@code int} value. 34 * If a value is present, {@code isPresent()} returns {@code true}. If no 35 * value is present, the object is considered <i>empty</i> and 36 * {@code isPresent()} returns {@code false}. 37 * 38 * <p>Additional methods that depend on the presence or absence of a contained 39 * value are provided, such as {@link #orElse(int) orElse()} 40 * (returns a default value if no value is present) and 41 * {@link #ifPresent(IntConsumer) ifPresent()} (performs an 42 * action if a value is present). 43 * 44 * <p>This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a> 45 * class; programmers should treat instances that are 46 * {@linkplain #equals(Object) equal} as interchangeable and should not 47 * use instances for synchronization, or unpredictable behavior may 48 * occur. For example, in a future release, synchronization may fail. 49 * 50 * @apiNote 51 * {@code OptionalInt} is primarily intended for use as a method return type where 52 * there is a clear need to represent "no result." A variable whose type is 53 * {@code OptionalInt} should never itself be {@code null}; it should always point 54 * to an {@code OptionalInt} instance. 55 * 56 * @since 1.8 57 */ 58 @jdk.internal.ValueBased 59 public final class OptionalInt { 60 /** 61 * Common instance for {@code empty()}. 62 */ 63 private static final OptionalInt EMPTY = new OptionalInt(); 64 65 /** 66 * If true then the value is present, otherwise indicates no value is present 67 */ 68 private final boolean isPresent; 69 private final int value; 70 71 /** 72 * Construct an empty instance. 73 * 74 * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY}, 75 * should exist per VM. 76 */ 77 private OptionalInt() { 78 this.isPresent = false; 79 this.value = 0; 80 } 81 82 /** 83 * Returns an empty {@code OptionalInt} instance. No value is present for 84 * this {@code OptionalInt}. 85 * 86 * @apiNote 87 * Though it may be tempting to do so, avoid testing if an object is empty 88 * by comparing with {@code ==} or {@code !=} against instances returned by 89 * {@code OptionalInt.empty()}. There is no guarantee that it is a singleton. 90 * Instead, use {@link #isEmpty()} or {@link #isPresent()}. 91 * 92 * @return an empty {@code OptionalInt} 93 */ 94 public static OptionalInt empty() { 95 return EMPTY; 96 } 97 98 /** 99 * Construct an instance with the described value. 100 * 101 * @param value the int value to describe 102 */ 103 private OptionalInt(int value) { 104 this.isPresent = true; 105 this.value = value; 106 } 107 108 /** 109 * Returns an {@code OptionalInt} describing the given value. 110 * 111 * @param value the value to describe 112 * @return an {@code OptionalInt} with the value present 113 */ 114 public static OptionalInt of(int value) { 115 return new OptionalInt(value); 116 } 117 118 /** 119 * If a value is present, returns the value, otherwise throws 120 * {@code NoSuchElementException}. 121 * 122 * @apiNote 123 * The preferred alternative to this method is {@link #orElseThrow()}. 124 * 125 * @return the value described by this {@code OptionalInt} 126 * @throws NoSuchElementException if no value is present 127 */ 128 public int getAsInt() { 129 if (!isPresent) { 130 throw new NoSuchElementException("No value present"); 131 } 132 return value; 133 } 134 135 /** 136 * If a value is present, returns {@code true}, otherwise {@code false}. 137 * 138 * @return {@code true} if a value is present, otherwise {@code false} 139 */ 140 public boolean isPresent() { 141 return isPresent; 142 } 143 144 /** 145 * If a value is not present, returns {@code true}, otherwise 146 * {@code false}. 147 * 148 * @return {@code true} if a value is not present, otherwise {@code false} 149 * @since 11 150 */ 151 public boolean isEmpty() { 152 return !isPresent; 153 } 154 155 /** 156 * If a value is present, performs the given action with the value, 157 * otherwise does nothing. 158 * 159 * @param action the action to be performed, if a value is present 160 * @throws NullPointerException if value is present and the given action is 161 * {@code null} 162 */ 163 public void ifPresent(IntConsumer action) { 164 if (isPresent) { 165 action.accept(value); 166 } 167 } 168 169 /** 170 * If a value is present, performs the given action with the value, 171 * otherwise performs the given empty-based action. 172 * 173 * @param action the action to be performed, if a value is present 174 * @param emptyAction the empty-based action to be performed, if no value is 175 * present 176 * @throws NullPointerException if a value is present and the given action 177 * is {@code null}, or no value is present and the given empty-based 178 * action is {@code null}. 179 * @since 9 180 */ 181 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) { 182 if (isPresent) { 183 action.accept(value); 184 } else { 185 emptyAction.run(); 186 } 187 } 188 189 /** 190 * If a value is present, returns a sequential {@link IntStream} containing 191 * only that value, otherwise returns an empty {@code IntStream}. 192 * 193 * @apiNote 194 * This method can be used to transform a {@code Stream} of optional 195 * integers to an {@code IntStream} of present integers: 196 * <pre>{@code 197 * Stream<OptionalInt> os = .. 198 * IntStream s = os.flatMapToInt(OptionalInt::stream) 199 * }</pre> 200 * 201 * @return the optional value as an {@code IntStream} 202 * @since 9 203 */ 204 public IntStream stream() { 205 if (isPresent) { 206 return IntStream.of(value); 207 } else { 208 return IntStream.empty(); 209 } 210 } 211 212 /** 213 * If a value is present, returns the value, otherwise returns 214 * {@code other}. 215 * 216 * @param other the value to be returned, if no value is present 217 * @return the value, if present, otherwise {@code other} 218 */ 219 public int orElse(int other) { 220 return isPresent ? value : other; 221 } 222 223 /** 224 * If a value is present, returns the value, otherwise returns the result 225 * produced by the supplying function. 226 * 227 * @param supplier the supplying function that produces a value to be returned 228 * @return the value, if present, otherwise the result produced by the 229 * supplying function 230 * @throws NullPointerException if no value is present and the supplying 231 * function is {@code null} 232 */ 233 public int orElseGet(IntSupplier supplier) { 234 return isPresent ? value : supplier.getAsInt(); 235 } 236 237 /** 238 * If a value is present, returns the value, otherwise throws 239 * {@code NoSuchElementException}. 240 * 241 * @return the value described by this {@code OptionalInt} 242 * @throws NoSuchElementException if no value is present 243 * @since 10 244 */ 245 public int orElseThrow() { 246 if (!isPresent) { 247 throw new NoSuchElementException("No value present"); 248 } 249 return value; 250 } 251 252 /** 253 * If a value is present, returns the value, otherwise throws an exception 254 * produced by the exception supplying function. 255 * 256 * @apiNote 257 * A method reference to the exception constructor with an empty argument 258 * list can be used as the supplier. For example, 259 * {@code IllegalStateException::new} 260 * 261 * @param <X> Type of the exception to be thrown 262 * @param exceptionSupplier the supplying function that produces an 263 * exception to be thrown 264 * @return the value, if present 265 * @throws X if no value is present 266 * @throws NullPointerException if no value is present and the exception 267 * supplying function is {@code null} 268 */ 269 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { 270 if (isPresent) { 271 return value; 272 } else { 273 throw exceptionSupplier.get(); 274 } 275 } 276 277 /** 278 * Indicates whether some other object is "equal to" this 279 * {@code OptionalInt}. The other object is considered equal if: 280 * <ul> 281 * <li>it is also an {@code OptionalInt} and; 282 * <li>both instances have no value present or; 283 * <li>the present values are "equal to" each other via {@code ==}. 284 * </ul> 285 * 286 * @param obj an object to be tested for equality 287 * @return {@code true} if the other object is "equal to" this object 288 * otherwise {@code false} 289 */ 290 @Override 291 public boolean equals(Object obj) { 292 if (this == obj) { 293 return true; 294 } 295 296 return obj instanceof OptionalInt other 297 && (isPresent && other.isPresent 298 ? value == other.value 299 : isPresent == other.isPresent); 300 } 301 302 /** 303 * Returns the hash code of the value, if present, otherwise {@code 0} 304 * (zero) if no value is present. 305 * 306 * @return hash code value of the present value or {@code 0} if no value is 307 * present 308 */ 309 @Override 310 public int hashCode() { 311 return isPresent ? Integer.hashCode(value) : 0; 312 } 313 314 /** 315 * Returns a non-empty string representation of this {@code OptionalInt} 316 * suitable for debugging. The exact presentation format is unspecified and 317 * may vary between implementations and versions. 318 * 319 * @implSpec 320 * If a value is present the result must include its string representation 321 * in the result. Empty and present {@code OptionalInt}s must be 322 * unambiguously differentiable. 323 * 324 * @return the string representation of this instance 325 */ 326 @Override 327 public String toString() { 328 return isPresent 329 ? ("OptionalInt[" + value + "]") 330 : "OptionalInt.empty"; 331 } 332 } --- EOF ---