1 /* 2 * Copyright (c) 2012, 2017, 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. If a 34 * value is present, {@code isPresent()} returns {@code true} and 35 * {@code getAsInt()} returns 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(int) orElse()} 39 * (returns a default value if no value is present) and 40 * {@link #ifPresent(IntConsumer) ifPresent()} (performs an 41 * action if a 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 OptionalInt} may have unpredictable results and should be avoided. 47 * 48 * @apiNote 49 * {@code OptionalInt} is primarily intended for use as a method return type where 50 * there is a clear need to represent "no result." A variable whose type is 51 * {@code OptionalInt} should never itself be {@code null}; it should always point 52 * to an {@code OptionalInt} instance. 53 * 54 * @since 1.8 55 */ 56 public final class OptionalInt { 57 /** 58 * Common instance for {@code empty()}. 59 */ 60 private static final OptionalInt EMPTY = new OptionalInt(); 61 62 /** 63 * If true then the value is present, otherwise indicates no value is present 64 */ 65 private final boolean isPresent; 66 private final int value; 67 68 /** 69 * Construct an empty instance. 70 * 71 * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY}, 72 * should exist per VM. 73 */ 74 private OptionalInt() { 75 this.isPresent = false; 76 this.value = 0; 77 } 78 79 /** 80 * Returns an empty {@code OptionalInt} instance. No value is present for 81 * this {@code OptionalInt}. 82 * 83 * @apiNote 84 * Though it may be tempting to do so, avoid testing if an object is empty 85 * by comparing with {@code ==} against instances returned by 86 * {@code OptionalInt.empty()}. There is no guarantee that it is a singleton. 87 * Instead, use {@link #isPresent()}. 88 * 89 * @return an empty {@code OptionalInt} 90 */ 91 public static OptionalInt empty() { 92 return EMPTY; 93 } 94 95 /** 96 * Construct an instance with the described value. 97 * 98 * @param value the int value to describe 99 */ 100 private OptionalInt(int value) { 101 this.isPresent = true; 102 this.value = value; 103 } 104 105 /** 106 * Returns an {@code OptionalInt} describing the given value. 107 * 108 * @param value the value to describe 109 * @return an {@code OptionalInt} with the value present 110 */ 111 public static OptionalInt of(int value) { 112 return new OptionalInt(value); 113 } 114 115 /** 116 * If a value is present, returns the value, otherwise throws 117 * {@code NoSuchElementException}. 118 * 119 * @apiNote 120 * The preferred alternative to this method is {@link #orElseThrow()}. 121 * 122 * @return the value described by this {@code OptionalInt} 123 * @throws NoSuchElementException if no value is present 124 */ 125 public int getAsInt() { 126 if (!isPresent) { 127 throw new NoSuchElementException("No value present"); 128 } 129 return value; 130 } 131 132 /** 133 * If a value is present, returns {@code true}, otherwise {@code false}. 134 * 135 * @return {@code true} if a value is present, otherwise {@code false} 136 */ 137 public boolean isPresent() { 138 return isPresent; 139 } 140 141 /** 142 * If a value is present, performs the given action with the value, 143 * otherwise does nothing. 144 * 145 * @param action the action to be performed, if a value is present 146 * @throws NullPointerException if value is present and the given action is 147 * {@code null} 148 */ 149 public void ifPresent(IntConsumer action) { 150 if (isPresent) { 151 action.accept(value); 152 } 153 } 154 155 /** 156 * If a value is present, performs the given action with the value, 157 * otherwise performs the given empty-based action. 158 * 159 * @param action the action to be performed, if a value is present 160 * @param emptyAction the empty-based action to be performed, if no value is 161 * present 162 * @throws NullPointerException if a value is present and the given action 163 * is {@code null}, or no value is present and the given empty-based 164 * action is {@code null}. 165 * @since 9 166 */ 167 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) { 168 if (isPresent) { 169 action.accept(value); 170 } else { 171 emptyAction.run(); 172 } 173 } 174 175 /** 176 * If a value is present, returns a sequential {@link IntStream} containing 177 * only that value, otherwise returns an empty {@code IntStream}. 178 * 179 * @apiNote 180 * This method can be used to transform a {@code Stream} of optional 181 * integers to an {@code IntStream} of present integers: 182 * <pre>{@code 183 * Stream<OptionalInt> os = .. 184 * IntStream s = os.flatMapToInt(OptionalInt::stream) 185 * }</pre> 186 * 187 * @return the optional value as an {@code IntStream} 188 * @since 9 189 */ 190 public IntStream stream() { 191 if (isPresent) { 192 return IntStream.of(value); 193 } else { 194 return IntStream.empty(); 195 } 196 } 197 198 /** 199 * If a value is present, returns the value, otherwise returns 200 * {@code other}. 201 * 202 * @param other the value to be returned, if no value is present 203 * @return the value, if present, otherwise {@code other} 204 */ 205 public int orElse(int other) { 206 return isPresent ? value : other; 207 } 208 209 /** 210 * If a value is present, returns the value, otherwise returns the result 211 * produced by the supplying function. 212 * 213 * @param supplier the supplying function that produces a value to be returned 214 * @return the value, if present, otherwise the result produced by the 215 * supplying function 216 * @throws NullPointerException if no value is present and the supplying 217 * function is {@code null} 218 */ 219 public int orElseGet(IntSupplier supplier) { 220 return isPresent ? value : supplier.getAsInt(); 221 } 222 223 /** 224 * If a value is present, returns the value, otherwise throws 225 * {@code NoSuchElementException}. 226 * 227 * @return the value described by this {@code OptionalInt} 228 * @throws NoSuchElementException if no value is present 229 * @since 10 230 */ 231 public int orElseThrow() { 232 if (!isPresent) { 233 throw new NoSuchElementException("No value present"); 234 } 235 return value; 236 } 237 238 /** 239 * If a value is present, returns the value, otherwise throws an exception 240 * produced by the exception supplying function. 241 * 242 * @apiNote 243 * A method reference to the exception constructor with an empty argument 244 * list can be used as the supplier. For example, 245 * {@code IllegalStateException::new} 246 * 247 * @param <X> Type of the exception to be thrown 248 * @param exceptionSupplier the supplying function that produces an 249 * exception to be thrown 250 * @return the value, if present 251 * @throws X if no value is present 252 * @throws NullPointerException if no value is present and the exception 253 * supplying function is {@code null} 254 */ 255 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { 256 if (isPresent) { 257 return value; 258 } else { 259 throw exceptionSupplier.get(); 260 } 261 } 262 263 /** 264 * Indicates whether some other object is "equal to" this 265 * {@code OptionalInt}. The other object is considered equal if: 266 * <ul> 267 * <li>it is also an {@code OptionalInt} and; 268 * <li>both instances have no value present or; 269 * <li>the present values are "equal to" each other via {@code ==}. 270 * </ul> 271 * 272 * @param obj an object to be tested for equality 273 * @return {@code true} if the other object is "equal to" this object 274 * otherwise {@code false} 275 */ 276 @Override 277 public boolean equals(Object obj) { 278 if (this == obj) { 279 return true; 280 } 281 282 if (!(obj instanceof OptionalInt)) { 283 return false; 284 } 285 286 OptionalInt other = (OptionalInt) obj; 287 return (isPresent && other.isPresent) 288 ? value == other.value 289 : isPresent == other.isPresent; 290 } 291 292 /** 293 * Returns the hash code of the value, if present, otherwise {@code 0} 294 * (zero) if no value is present. 295 * 296 * @return hash code value of the present value or {@code 0} if no value is 297 * present 298 */ 299 @Override 300 public int hashCode() { 301 return isPresent ? Integer.hashCode(value) : 0; 302 } 303 304 /** 305 * Returns a non-empty string representation of this {@code OptionalInt} 306 * suitable for debugging. The exact presentation format is unspecified and 307 * may vary between implementations and versions. 308 * 309 * @implSpec 310 * If a value is present the result must include its string representation 311 * in the result. Empty and present {@code OptionalInt}s must be 312 * unambiguously differentiable. 313 * 314 * @return the string representation of this instance 315 */ 316 @Override 317 public String toString() { 318 return isPresent 319 ? String.format("OptionalInt[%s]", value) 320 : "OptionalInt.empty"; 321 } 322 }