1/* 2 * Copyright (c) 2012, 2013, 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 */ 25package java.util; 26 27import java.util.function.DoubleConsumer; 28import java.util.function.DoubleSupplier; 29import java.util.function.Supplier; 30 31/** 32 * A container object which may or may not contain a {@code double} value. 33 * If a value is present, {@code isPresent()} will return {@code true} and 34 * {@code getAsDouble()} will return the value. 35 * 36 * <p>Additional methods that depend on the presence or absence of a contained 37 * value are provided, such as {@link #orElse(double) orElse()} 38 * (return a default value if value not present) and 39 * {@link #ifPresent(java.util.function.DoubleConsumer) ifPresent()} (execute a block 40 * of code if the value is present). 41 * 42 * @since 1.8 43 */ 44public final class OptionalDouble { 45 /** 46 * Common instance for {@code empty()}. 47 */ 48 private static final OptionalDouble EMPTY = new OptionalDouble(); 49 50 /** 51 * If true then the value is present, otherwise indicates no value is present 52 */ 53 private final boolean isPresent; 54 private final double value; 55 56 /** 57 * Construct an empty instance. 58 * 59 * @implNote generally only one empty instance, {@link OptionalDouble#EMPTY}, 60 * should exist per VM. 61 */ 62 private OptionalDouble() { 63 this.isPresent = false; 64 this.value = Double.NaN; 65 } 66 67 /** 68 * Returns an empty {@code OptionalDouble} instance. No value is present for this 69 * OptionalDouble. 70 * 71 * @apiNote Though it may be tempting to do so, avoid testing if an object 72 * is empty by comparing with {@code ==} against instances returned by 73 * {@code Option.empty()}. There is no guarantee that it is a singleton. 74 * Instead, use {@link #isPresent()}. 75 * 76 * @return an empty {@code OptionalDouble}. 77 */ 78 public static OptionalDouble empty() { 79 return EMPTY; 80 } 81 82 /** 83 * Construct an instance with the value present. 84 * 85 * @param value the double value to be present. 86 */ 87 private OptionalDouble(double value) { 88 this.isPresent = true; 89 this.value = value; 90 } 91 92 /** 93 * Return an {@code OptionalDouble} with the specified value present. 94 * 95 * @param value the value to be present 96 * @return an {@code OptionalDouble} with the value present 97 */ 98 public static OptionalDouble of(double value) { 99 return new OptionalDouble(value); 100 } 101 102 /** 103 * If a value is present in this {@code OptionalDouble}, returns the value, 104 * otherwise throws {@code NoSuchElementException}. 105 * 106 * @return the value held by this {@code OptionalDouble} 107 * @throws NoSuchElementException if there is no value present 108 * 109 * @see OptionalDouble#isPresent() 110 */ 111 public double getAsDouble() { 112 if (!isPresent) { 113 throw new NoSuchElementException("No value present"); 114 } 115 return value; 116 } 117 118 /** 119 * Return {@code true} if there is a value present, otherwise {@code false}. 120 * 121 * @return {@code true} if there is a value present, otherwise {@code false} 122 */ 123 public boolean isPresent() { 124 return isPresent; 125 } 126 127 /** 128 * Have the specified consumer accept the value if a value is present, 129 * otherwise do nothing. 130 * 131 * @param consumer block to be executed if a value is present 132 * @throws NullPointerException if value is present and {@code consumer} is 133 * null 134 */ 135 public void ifPresent(DoubleConsumer consumer) { 136 if (isPresent) 137 consumer.accept(value); 138 } 139 140 /** 141 * Return the value if present, otherwise return {@code other}. 142 * 143 * @param other the value to be returned if there is no value present 144 * @return the value, if present, otherwise {@code other} 145 */ 146 public double orElse(double other) { 147 return isPresent ? value : other; 148 } 149 150 /** 151 * Return the value if present, otherwise invoke {@code other} and return 152 * the result of that invocation. 153 * 154 * @param other a {@code DoubleSupplier} whose result is returned if no value 155 * is present 156 * @return the value if present otherwise the result of {@code other.getAsDouble()} 157 * @throws NullPointerException if value is not present and {@code other} is 158 * null 159 */ 160 public double orElseGet(DoubleSupplier other) { 161 return isPresent ? value : other.getAsDouble(); 162 } 163 164 /** 165 * Return the contained value, if present, otherwise throw an exception 166 * to be created by the provided supplier. 167 * 168 * @apiNote A method reference to the exception constructor with an empty 169 * argument list can be used as the supplier. For example, 170 * {@code IllegalStateException::new} 171 * 172 * @param <X> Type of the exception to be thrown 173 * @param exceptionSupplier The supplier which will return the exception to 174 * be thrown 175 * @return the present value 176 * @throws X if there is no value present 177 * @throws NullPointerException if no value is present and 178 * {@code exceptionSupplier} is null 179 */ 180 public<X extends Throwable> double orElseThrow(Supplier<X> exceptionSupplier) throws X { 181 if (isPresent) { 182 return value; 183 } else { 184 throw exceptionSupplier.get(); 185 } 186 } 187 188 /** 189 * Indicates whether some other object is "equal to" this OptionalDouble. The 190 * other object is considered equal if: 191 * <ul> 192 * <li>it is also an {@code OptionalDouble} and; 193 * <li>both instances have no value present or; 194 * <li>the present values are "equal to" each other via {@code Double.compare() == 0}. 195 * </ul> 196 * 197 * @param obj an object to be tested for equality 198 * @return {code true} if the other object is "equal to" this object 199 * otherwise {@code false} 200 */ 201 @Override 202 public boolean equals(Object obj) { 203 if (this == obj) { 204 return true; 205 } 206 207 if (!(obj instanceof OptionalDouble)) { 208 return false; 209 } 210 211 OptionalDouble other = (OptionalDouble) obj; 212 return (isPresent && other.isPresent) 213 ? Double.compare(value, other.value) == 0 214 : isPresent == other.isPresent; 215 } 216 217 /** 218 * Returns the hash code value of the present value, if any, or 0 (zero) if 219 * no value is present. 220 * 221 * @return hash code value of the present value or 0 if no value is present 222 */ 223 @Override 224 public int hashCode() { 225 return isPresent ? Double.hashCode(value) : 0; 226 } 227 228 /** 229 * {@inheritDoc} 230 * 231 * Returns a non-empty string representation of this object suitable for 232 * debugging. The exact presentation format is unspecified and may vary 233 * between implementations and versions. 234 * 235 * @implSpec If a value is present the result must include its string 236 * representation in the result. Empty and present instances must be 237 * unambiguously differentiable. 238 * 239 * @return the string representation of this instance 240 */ 241 @Override 242 public String toString() { 243 return isPresent 244 ? String.format("OptionalDouble[%s]", value) 245 : "OptionalDouble.empty"; 246 } 247} 248