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 methods {@link #orElse(int) orElse} and 121 * {@link #orElseGet(IntSupplier) orElseGet} 122 * are generally preferable to this method, as they return a substitute 123 * value if the value is absent, instead of throwing an exception. 124 * 125 * @return the value described by this {@code OptionalInt} 126 * @throws NoSuchElementException if no value is present 127 * @see OptionalInt#isPresent() 128 */ 129 public int getAsInt() { 130 if (!isPresent) { 131 throw new NoSuchElementException("No value present"); 132 } 133 return value; 134 } 135 136 /** 137 * If a value is present, returns {@code true}, otherwise {@code false}. 138 * 139 * @return {@code true} if a value is present, otherwise {@code false} 140 */ 141 public boolean isPresent() { 142 return isPresent; 143 } 144 145 /** 146 * If a value is present, performs the given action with the value, 147 * otherwise does nothing. 148 * 149 * @param action the action to be performed, if a value is present 150 * @throws NullPointerException if value is present and the given action is 151 * {@code null} 152 */ 153 public void ifPresent(IntConsumer action) { 154 if (isPresent) { 155 action.accept(value); 156 } 157 } 158 159 /** 160 * If a value is present, performs the given action with the value, 161 * otherwise performs the given empty-based action. 162 * 163 * @param action the action to be performed, if a value is present 164 * @param emptyAction the empty-based action to be performed, if no value is 165 * present 166 * @throws NullPointerException if a value is present and the given action 167 * is {@code null}, or no value is present and the given empty-based 168 * action is {@code null}. 169 * @since 9 170 */ 171 public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) { 172 if (isPresent) { 173 action.accept(value); 174 } else { 175 emptyAction.run(); 176 } 177 } 178 179 /** 180 * If a value is present, returns a sequential {@link IntStream} containing 181 * only that value, otherwise returns an empty {@code IntStream}. 182 * 183 * @apiNote 184 * This method can be used to transform a {@code Stream} of optional 185 * integers to an {@code IntStream} of present integers: 186 * <pre>{@code 187 * Stream<OptionalInt> os = .. 188 * IntStream s = os.flatMapToInt(OptionalInt::stream) 189 * }</pre> 190 * 191 * @return the optional value as an {@code IntStream} 192 * @since 9 193 */ 194 public IntStream stream() { 195 if (isPresent) { 196 return IntStream.of(value); 197 } else { 198 return IntStream.empty(); 199 } 200 } 201 202 /** 203 * If a value is present, returns the value, otherwise returns 204 * {@code other}. 205 * 206 * @param other the value to be returned, if no value is present 207 * @return the value, if present, otherwise {@code other} 208 */ 209 public int orElse(int other) { 210 return isPresent ? value : other; 211 } 212 213 /** 214 * If a value is present, returns the value, otherwise returns the result 215 * produced by the supplying function. 216 * 217 * @param supplier the supplying function that produces a value to be returned 218 * @return the value, if present, otherwise the result produced by the 219 * supplying function 220 * @throws NullPointerException if no value is present and the supplying 221 * function is {@code null} 222 */ 223 public int orElseGet(IntSupplier supplier) { 224 return isPresent ? value : supplier.getAsInt(); 225 } 226 227 /** 228 * If a value is present, returns the value, otherwise throws an exception 229 * produced by the exception supplying function. 230 * 231 * @apiNote 232 * A method reference to the exception constructor with an empty argument 233 * list can be used as the supplier. For example, 234 * {@code IllegalStateException::new} 235 * 236 * @param <X> Type of the exception to be thrown 237 * @param exceptionSupplier the supplying function that produces an 238 * exception to be thrown 239 * @return the value, if present 240 * @throws X if no value is present 241 * @throws NullPointerException if no value is present and the exception 242 * supplying function is {@code null} 243 */ 244 public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { 245 if (isPresent) { 246 return value; 247 } else { 248 throw exceptionSupplier.get(); 249 } 250 } 251 252 /** 253 * Indicates whether some other object is "equal to" this 254 * {@code OptionalInt}. The other object is considered equal if: 255 * <ul> 256 * <li>it is also an {@code OptionalInt} and; 257 * <li>both instances have no value present or; 258 * <li>the present values are "equal to" each other via {@code ==}. 259 * </ul> 260 * 261 * @param obj an object to be tested for equality 262 * @return {@code true} if the other object is "equal to" this object 263 * otherwise {@code false} 264 */ 265 @Override 266 public boolean equals(Object obj) { 267 if (this == obj) { 268 return true; 269 } 270 271 if (!(obj instanceof OptionalInt)) { 272 return false; 273 } 274 275 OptionalInt other = (OptionalInt) obj; 276 return (isPresent && other.isPresent) 277 ? value == other.value 278 : isPresent == other.isPresent; 279 } 280 281 /** 282 * Returns the hash code of the value, if present, otherwise {@code 0} 283 * (zero) if no value is present. 284 * 285 * @return hash code value of the present value or {@code 0} if no value is 286 * present 287 */ 288 @Override 289 public int hashCode() { 290 return isPresent ? Integer.hashCode(value) : 0; 291 } 292 293 /** 294 * Returns a non-empty string representation of this {@code OptionalInt} 295 * suitable for debugging. The exact presentation format is unspecified and 296 * may vary between implementations and versions. 297 * 298 * @implSpec 299 * If a value is present the result must include its string representation 300 * in the result. Empty and present {@code OptionalInt}s must be 301 * unambiguously differentiable. 302 * 303 * @return the string representation of this instance 304 */ 305 @Override 306 public String toString() { 307 return isPresent 308 ? String.format("OptionalInt[%s]", value) 309 : "OptionalInt.empty"; 310 } 311 }