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