1 /* 2 * Copyright (c) 2012, 2018, 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.DoubleConsumer; 28 import java.util.function.DoubleSupplier; 29 import java.util.function.Supplier; 30 import java.util.stream.DoubleStream; 31 32 // Android-changed: removed ValueBased paragraph. 33 /** 34 * A container object which may or may not contain a {@code double} value. 35 * If a value is present, {@code isPresent()} returns {@code true}. If no 36 * value is present, the object is considered <i>empty</i> and 37 * {@code isPresent()} returns {@code false}. 38 * 39 * <p>Additional methods that depend on the presence or absence of a contained 40 * value are provided, such as {@link #orElse(double) orElse()} 41 * (returns a default value if no value is present) and 42 * {@link #ifPresent(DoubleConsumer) ifPresent()} (performs 43 * an action if a value is present). 44 * 45 * @apiNote 46 * {@code OptionalDouble} is primarily intended for use as a method return type where 47 * there is a clear need to represent "no result." A variable whose type is 48 * {@code OptionalDouble} should never itself be {@code null}; it should always point 49 * to an {@code OptionalDouble} instance. 50 * 51 * @since 1.8 52 */ 53 public final class OptionalDouble { 54 /** 55 * Common instance for {@code empty()}. 56 */ 57 private static final OptionalDouble EMPTY = new OptionalDouble(); 58 59 /** 60 * If true then the value is present, otherwise indicates no value is present 61 */ 62 private final boolean isPresent; 63 private final double value; 64 65 /** 66 * Construct an empty instance. 67 * 68 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY}, 69 * should exist per VM. 70 */ OptionalDouble()71 private OptionalDouble() { 72 this.isPresent = false; 73 this.value = Double.NaN; 74 } 75 76 /** 77 * Returns an empty {@code OptionalDouble} instance. No value is present 78 * for this {@code OptionalDouble}. 79 * 80 * @apiNote 81 * Though it may be tempting to do so, avoid testing if an object is empty 82 * by comparing with {@code ==} against instances returned by 83 * {@code OptionalDouble.empty()}. There is no guarantee that it is a singleton. 84 * Instead, use {@link #isPresent()}. 85 * 86 * @return an empty {@code OptionalDouble}. 87 */ empty()88 public static OptionalDouble empty() { 89 return EMPTY; 90 } 91 92 /** 93 * Construct an instance with the described value. 94 * 95 * @param value the double value to describe. 96 */ OptionalDouble(double value)97 private OptionalDouble(double value) { 98 this.isPresent = true; 99 this.value = value; 100 } 101 102 /** 103 * Returns an {@code OptionalDouble} describing the given value. 104 * 105 * @param value the value to describe 106 * @return an {@code OptionalDouble} with the value present 107 */ of(double value)108 public static OptionalDouble of(double value) { 109 return new OptionalDouble(value); 110 } 111 112 /** 113 * If a value is present, returns the value, otherwise throws 114 * {@code NoSuchElementException}. 115 * 116 * @apiNote 117 * The preferred alternative to this method is {@link #orElseThrow()}. 118 * 119 * @return the value described by this {@code OptionalDouble} 120 * @throws NoSuchElementException if no value is present 121 */ getAsDouble()122 public double getAsDouble() { 123 if (!isPresent) { 124 throw new NoSuchElementException("No value present"); 125 } 126 return value; 127 } 128 129 /** 130 * If a value is present, returns {@code true}, otherwise {@code false}. 131 * 132 * @return {@code true} if a value is present, otherwise {@code false} 133 */ isPresent()134 public boolean isPresent() { 135 return isPresent; 136 } 137 138 /** 139 * If a value is not present, returns {@code true}, otherwise 140 * {@code false}. 141 * 142 * @return {@code true} if a value is not present, otherwise {@code false} 143 * @since 11 144 */ isEmpty()145 public boolean isEmpty() { 146 return !isPresent; 147 } 148 149 /** 150 * If a value is present, performs the given action with the value, 151 * otherwise does nothing. 152 * 153 * @param action the action to be performed, if a value is present 154 * @throws NullPointerException if value is present and the given action is 155 * {@code null} 156 */ ifPresent(DoubleConsumer action)157 public void ifPresent(DoubleConsumer action) { 158 if (isPresent) { 159 action.accept(value); 160 } 161 } 162 163 /** 164 * If a value is present, performs the given action with the value, 165 * otherwise performs the given empty-based action. 166 * 167 * @param action the action to be performed, if a value is present 168 * @param emptyAction the empty-based action to be performed, if no value is 169 * present 170 * @throws NullPointerException if a value is present and the given action 171 * is {@code null}, or no value is present and the given empty-based 172 * action is {@code null}. 173 * @since 9 174 */ ifPresentOrElse(DoubleConsumer action, Runnable emptyAction)175 public void ifPresentOrElse(DoubleConsumer action, Runnable emptyAction) { 176 if (isPresent) { 177 action.accept(value); 178 } else { 179 emptyAction.run(); 180 } 181 } 182 183 /** 184 * If a value is present, returns a sequential {@link DoubleStream} 185 * containing only that value, otherwise returns an empty 186 * {@code DoubleStream}. 187 * 188 * @apiNote 189 * This method can be used to transform a {@code Stream} of optional doubles 190 * to a {@code DoubleStream} of present doubles: 191 * <pre>{@code 192 * Stream<OptionalDouble> os = .. 193 * DoubleStream s = os.flatMapToDouble(OptionalDouble::stream) 194 * }</pre> 195 * 196 * @return the optional value as a {@code DoubleStream} 197 * @since 9 198 */ stream()199 public DoubleStream stream() { 200 if (isPresent) { 201 return DoubleStream.of(value); 202 } else { 203 return DoubleStream.empty(); 204 } 205 } 206 207 /** 208 * If a value is present, returns the value, otherwise returns 209 * {@code other}. 210 * 211 * @param other the value to be returned, if no value is present 212 * @return the value, if present, otherwise {@code other} 213 */ orElse(double other)214 public double orElse(double other) { 215 return isPresent ? value : other; 216 } 217 218 /** 219 * If a value is present, returns the value, otherwise returns the result 220 * produced by the supplying function. 221 * 222 * @param supplier the supplying function that produces a value to be returned 223 * @return the value, if present, otherwise the result produced by the 224 * supplying function 225 * @throws NullPointerException if no value is present and the supplying 226 * function is {@code null} 227 */ orElseGet(DoubleSupplier supplier)228 public double orElseGet(DoubleSupplier supplier) { 229 return isPresent ? value : supplier.getAsDouble(); 230 } 231 232 /** 233 * If a value is present, returns the value, otherwise throws 234 * {@code NoSuchElementException}. 235 * 236 * @return the value described by this {@code OptionalDouble} 237 * @throws NoSuchElementException if no value is present 238 * @since 10 239 */ orElseThrow()240 public double orElseThrow() { 241 if (!isPresent) { 242 throw new NoSuchElementException("No value present"); 243 } 244 return value; 245 } 246 247 /** 248 * If a value is present, returns the value, otherwise throws an exception 249 * produced by the exception supplying function. 250 * 251 * @apiNote 252 * A method reference to the exception constructor with an empty argument 253 * list can be used as the supplier. For example, 254 * {@code IllegalStateException::new} 255 * 256 * @param <X> Type of the exception to be thrown 257 * @param exceptionSupplier the supplying function that produces an 258 * exception to be thrown 259 * @return the value, if present 260 * @throws X if no value is present 261 * @throws NullPointerException if no value is present and the exception 262 * supplying function is {@code null} 263 */ orElseThrow(Supplier<? extends X> exceptionSupplier)264 public<X extends Throwable> double orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { 265 if (isPresent) { 266 return value; 267 } else { 268 throw exceptionSupplier.get(); 269 } 270 } 271 272 /** 273 * Indicates whether some other object is "equal to" this 274 * {@code OptionalDouble}. The other object is considered equal if: 275 * <ul> 276 * <li>it is also an {@code OptionalDouble} and; 277 * <li>both instances have no value present or; 278 * <li>the present values are "equal to" each other via 279 * {@code Double.compare() == 0}. 280 * </ul> 281 * 282 * @param obj an object to be tested for equality 283 * @return {@code true} if the other object is "equal to" this object 284 * otherwise {@code false} 285 */ 286 @Override equals(Object obj)287 public boolean equals(Object obj) { 288 if (this == obj) { 289 return true; 290 } 291 292 if (!(obj instanceof OptionalDouble)) { 293 return false; 294 } 295 296 OptionalDouble other = (OptionalDouble) obj; 297 return (isPresent && other.isPresent) 298 ? Double.compare(value, other.value) == 0 299 : 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 hashCode()310 public int hashCode() { 311 return isPresent ? Double.hashCode(value) : 0; 312 } 313 314 /** 315 * Returns a non-empty string representation of this {@code OptionalDouble} 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 OptionalDouble}s must be 322 * unambiguously differentiable. 323 * 324 * @return the string representation of this instance 325 */ 326 @Override toString()327 public String toString() { 328 return isPresent 329 ? String.format("OptionalDouble[%s]", value) 330 : "OptionalDouble.empty"; 331 } 332 } 333