1 /*
   2  * Copyright (c) 2012, 2015, 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.
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  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 a {@code int} value.
  34  * If a value is present, {@code isPresent()} will return {@code true} and
  35  * {@code getAsInt()} will return 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  * (return a default value if value not present) and
  40  * {@link #ifPresent(java.util.function.IntConsumer) ifPresent()} (execute a block
  41  * of code if the 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  * @since 1.8
  49  */
  50 public final class OptionalInt {
  51     /**
  52      * Common instance for {@code empty()}.
  53      */
  54     private static final OptionalInt EMPTY = new OptionalInt();
  55 
  56     /**
  57      * If true then the value is present, otherwise indicates no value is present
  58      */
  59     private final boolean isPresent;
  60     private final int value;
  61 
  62     /**
  63      * Construct an empty instance.
  64      *
  65      * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
  66      * should exist per VM.
  67      */
  68     private OptionalInt() {
  69         this.isPresent = false;
  70         this.value = 0;
  71     }
  72 
  73     /**
  74      * Returns an empty {@code OptionalInt} instance.  No value is present for this
  75      * OptionalInt.
  76      *
  77      * @apiNote Though it may be tempting to do so, avoid testing if an object
  78      * is empty by comparing with {@code ==} against instances returned by
  79      * {@code Option.empty()}. There is no guarantee that it is a singleton.
  80      * Instead, use {@link #isPresent()}.
  81      *
  82      *  @return an empty {@code OptionalInt}
  83      */
  84     public static OptionalInt empty() {
  85         return EMPTY;
  86     }
  87 
  88     /**
  89      * Construct an instance with the value present.
  90      *
  91      * @param value the int value to be present
  92      */
  93     private OptionalInt(int value) {
  94         this.isPresent = true;
  95         this.value = value;
  96     }
  97 
  98     /**
  99      * Return an {@code OptionalInt} with the specified value present.
 100      *
 101      * @param value the value to be present
 102      * @return an {@code OptionalInt} with the value present
 103      */
 104     public static OptionalInt of(int value) {
 105         return new OptionalInt(value);
 106     }
 107 
 108     /**
 109      * If a value is present in this {@code OptionalInt}, returns the value,
 110      * otherwise throws {@code NoSuchElementException}.
 111      *
 112      * @return the value held by this {@code OptionalInt}
 113      * @throws NoSuchElementException if there is no value present
 114      *
 115      * @see OptionalInt#isPresent()
 116      */
 117     public int getAsInt() {
 118         if (!isPresent) {
 119             throw new NoSuchElementException("No value present");
 120         }
 121         return value;
 122     }
 123 
 124     /**
 125      * Return {@code true} if there is a value present, otherwise {@code false}.
 126      *
 127      * @return {@code true} if there is a value present, otherwise {@code false}
 128      */
 129     public boolean isPresent() {
 130         return isPresent;
 131     }
 132 
 133     /**
 134      * Have the specified consumer accept the value if a value is present,
 135      * otherwise do nothing.
 136      *
 137      * @param consumer block to be executed if a value is present
 138      * @throws NullPointerException if value is present and {@code consumer} is
 139      * null
 140      */
 141     public void ifPresent(IntConsumer consumer) {
 142         if (isPresent) {
 143             consumer.accept(value);
 144         }
 145     }
 146 
 147     /**
 148      * If a value is present return a sequential {@link IntStream} containing
 149      * only that value, otherwise return an empty {@code IntStream}.
 150      *
 151      * @apiNote This method can be used to transform a {@code Stream} of
 152      * optional integers to an {@code IntStream} of present integers:
 153      *
 154      * <pre>{@code
 155      *     Stream<OptionalInt> os = ..
 156      *     IntStream s = os.flatMapToInt(OptionalInt::stream)
 157      * }</pre>
 158      *
 159      * @return the optional value as an {@code IntStream}
 160      * @since 1.9
 161      */
 162     public IntStream stream() {
 163         if (isPresent) {
 164             return IntStream.of(value);
 165         } else {
 166             return IntStream.empty();
 167         }
 168     }
 169 
 170     /**
 171      * Return the value if present, otherwise return {@code other}.
 172      *
 173      * @param other the value to be returned if there is no value present
 174      * @return the value, if present, otherwise {@code other}
 175      */
 176     public int orElse(int other) {
 177         return isPresent ? value : other;
 178     }
 179 
 180     /**
 181      * Return the value if present, otherwise invoke {@code other} and return
 182      * the result of that invocation.
 183      *
 184      * @param other a {@code IntSupplier} whose result is returned if no value
 185      * is present
 186      * @return the value if present otherwise the result of {@code other.getAsInt()}
 187      * @throws NullPointerException if value is not present and {@code other} is
 188      * null
 189      */
 190     public int orElseGet(IntSupplier other) {
 191         return isPresent ? value : other.getAsInt();
 192     }
 193 
 194     /**
 195      * Return the contained value, if present, otherwise throw an exception
 196      * to be created by the provided supplier.
 197      *
 198      * @apiNote A method reference to the exception constructor with an empty
 199      * argument list can be used as the supplier. For example,
 200      * {@code IllegalStateException::new}
 201      *
 202      * @param <X> Type of the exception to be thrown
 203      * @param exceptionSupplier The supplier which will return the exception to
 204      * be thrown
 205      * @return the present value
 206      * @throws X if there is no value present
 207      * @throws NullPointerException if no value is present and
 208      * {@code exceptionSupplier} is null
 209      */
 210     public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
 211         if (isPresent) {
 212             return value;
 213         } else {
 214             throw exceptionSupplier.get();
 215         }
 216     }
 217 
 218     /**
 219      * Indicates whether some other object is "equal to" this OptionalInt. The
 220      * other object is considered equal if:
 221      * <ul>
 222      * <li>it is also an {@code OptionalInt} and;
 223      * <li>both instances have no value present or;
 224      * <li>the present values are "equal to" each other via {@code ==}.
 225      * </ul>
 226      *
 227      * @param obj an object to be tested for equality
 228      * @return {code true} if the other object is "equal to" this object
 229      * otherwise {@code false}
 230      */
 231     @Override
 232     public boolean equals(Object obj) {
 233         if (this == obj) {
 234             return true;
 235         }
 236 
 237         if (!(obj instanceof OptionalInt)) {
 238             return false;
 239         }
 240 
 241         OptionalInt other = (OptionalInt) obj;
 242         return (isPresent && other.isPresent)
 243                 ? value == other.value
 244                 : isPresent == other.isPresent;
 245     }
 246 
 247     /**
 248      * Returns the hash code value of the present value, if any, or 0 (zero) if
 249      * no value is present.
 250      *
 251      * @return hash code value of the present value or 0 if no value is present
 252      */
 253     @Override
 254     public int hashCode() {
 255         return isPresent ? Integer.hashCode(value) : 0;
 256     }
 257 
 258     /**
 259      * {@inheritDoc}
 260      *
 261      * Returns a non-empty string representation of this object suitable for
 262      * debugging. The exact presentation format is unspecified and may vary
 263      * between implementations and versions.
 264      *
 265      * @implSpec If a value is present the result must include its string
 266      * representation in the result. Empty and present instances must be
 267      * unambiguously differentiable.
 268      *
 269      * @return the string representation of this instance
 270      */
 271     @Override
 272     public String toString() {
 273         return isPresent
 274                 ? String.format("OptionalInt[%s]", value)
 275                 : "OptionalInt.empty";
 276     }
 277 }