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.
  34  * If a value is present, {@code isPresent()} returns {@code true}. If no
  35  * value is present, the object is considered <i>empty</i> and
  36  * {@code isPresent()} returns {@code false}.
  37  *
  38  * <p>Additional methods that depend on the presence or absence of a contained
  39  * value are provided, such as {@link #orElse(int) orElse()}
  40  * (returns a default value if no value is present) and
  41  * {@link #ifPresent(IntConsumer) ifPresent()} (performs an
  42  * action if a value is present).
  43  *
  44  * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
  45  * class; use of identity-sensitive operations (including reference equality
  46  * ({@code ==}), identity hash code, or synchronization) on instances of
  47  * {@code OptionalInt} may have unpredictable results and should be avoided.
  48  *
  49  * @apiNote
  50  * {@code OptionalInt} is primarily intended for use as a method return type where
  51  * there is a clear need to represent "no result." A variable whose type is
  52  * {@code OptionalInt} should never itself be {@code null}; it should always point
  53  * to an {@code OptionalInt} 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 preferred alternative to this method is {@link #orElseThrow()}.
 122      *
 123      * @return the value described by this {@code OptionalInt}
 124      * @throws NoSuchElementException if no value is present
 125      */
 126     public int getAsInt() {
 127         if (!isPresent) {
 128             throw new NoSuchElementException("No value present");
 129         }
 130         return value;
 131     }
 132 
 133     /**
 134      * If a value is present, returns {@code true}, otherwise {@code false}.
 135      *
 136      * @return {@code true} if a value is present, otherwise {@code false}
 137      */
 138     public boolean isPresent() {
 139         return isPresent;
 140     }
 141 
 142     /**
 143      * If a value is present, performs the given action with the value,
 144      * otherwise does nothing.
 145      *
 146      * @param action the action to be performed, if a value is present
 147      * @throws NullPointerException if value is present and the given action is
 148      *         {@code null}
 149      */
 150     public void ifPresent(IntConsumer action) {
 151         if (isPresent) {
 152             action.accept(value);
 153         }
 154     }
 155 
 156     /**
 157      * If a value is present, performs the given action with the value,
 158      * otherwise performs the given empty-based action.
 159      *
 160      * @param action the action to be performed, if a value is present
 161      * @param emptyAction the empty-based action to be performed, if no value is
 162      *        present
 163      * @throws NullPointerException if a value is present and the given action
 164      *         is {@code null}, or no value is present and the given empty-based
 165      *         action is {@code null}.
 166      * @since 9
 167      */
 168     public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
 169         if (isPresent) {
 170             action.accept(value);
 171         } else {
 172             emptyAction.run();
 173         }
 174     }
 175 
 176     /**
 177      * If a value is present, returns a sequential {@link IntStream} containing
 178      * only that value, otherwise returns an empty {@code IntStream}.
 179      *
 180      * @apiNote
 181      * This method can be used to transform a {@code Stream} of optional
 182      * integers to an {@code IntStream} of present integers:
 183      * <pre>{@code
 184      *     Stream<OptionalInt> os = ..
 185      *     IntStream s = os.flatMapToInt(OptionalInt::stream)
 186      * }</pre>
 187      *
 188      * @return the optional value as an {@code IntStream}
 189      * @since 9
 190      */
 191     public IntStream stream() {
 192         if (isPresent) {
 193             return IntStream.of(value);
 194         } else {
 195             return IntStream.empty();
 196         }
 197     }
 198 
 199     /**
 200      * If a value is present, returns the value, otherwise returns
 201      * {@code other}.
 202      *
 203      * @param other the value to be returned, if no value is present
 204      * @return the value, if present, otherwise {@code other}
 205      */
 206     public int orElse(int other) {
 207         return isPresent ? value : other;
 208     }
 209 
 210     /**
 211      * If a value is present, returns the value, otherwise returns the result
 212      * produced by the supplying function.
 213      *
 214      * @param supplier the supplying function that produces a value to be returned
 215      * @return the value, if present, otherwise the result produced by the
 216      *         supplying function
 217      * @throws NullPointerException if no value is present and the supplying
 218      *         function is {@code null}
 219      */
 220     public int orElseGet(IntSupplier supplier) {
 221         return isPresent ? value : supplier.getAsInt();
 222     }
 223 
 224     /**
 225      * If a value is present, returns the value, otherwise throws
 226      * {@code NoSuchElementException}.
 227      *
 228      * @return the value described by this {@code OptionalInt}
 229      * @throws NoSuchElementException if no value is present
 230      * @since 10
 231      */
 232     public int orElseThrow() {
 233         if (!isPresent) {
 234             throw new NoSuchElementException("No value present");
 235         }
 236         return value;
 237     }
 238 
 239     /**
 240      * If a value is present, returns the value, otherwise throws an exception
 241      * produced by the exception supplying function.
 242      *
 243      * @apiNote
 244      * A method reference to the exception constructor with an empty argument
 245      * list can be used as the supplier. For example,
 246      * {@code IllegalStateException::new}
 247      *
 248      * @param <X> Type of the exception to be thrown
 249      * @param exceptionSupplier the supplying function that produces an
 250      *        exception to be thrown
 251      * @return the value, if present
 252      * @throws X if no value is present
 253      * @throws NullPointerException if no value is present and the exception
 254      *         supplying function is {@code null}
 255      */
 256     public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
 257         if (isPresent) {
 258             return value;
 259         } else {
 260             throw exceptionSupplier.get();
 261         }
 262     }
 263 
 264     /**
 265      * Indicates whether some other object is "equal to" this
 266      * {@code OptionalInt}.  The other object is considered equal if:
 267      * <ul>
 268      * <li>it is also an {@code OptionalInt} and;
 269      * <li>both instances have no value present or;
 270      * <li>the present values are "equal to" each other via {@code ==}.
 271      * </ul>
 272      *
 273      * @param obj an object to be tested for equality
 274      * @return {@code true} if the other object is "equal to" this object
 275      *         otherwise {@code false}
 276      */
 277     @Override
 278     public boolean equals(Object obj) {
 279         if (this == obj) {
 280             return true;
 281         }
 282 
 283         if (!(obj instanceof OptionalInt)) {
 284             return false;
 285         }
 286 
 287         OptionalInt other = (OptionalInt) obj;
 288         return (isPresent && other.isPresent)
 289                 ? value == other.value
 290                 : isPresent == other.isPresent;
 291     }
 292 
 293     /**
 294      * Returns the hash code of the value, if present, otherwise {@code 0}
 295      * (zero) if no value is present.
 296      *
 297      * @return hash code value of the present value or {@code 0} if no value is
 298      *         present
 299      */
 300     @Override
 301     public int hashCode() {
 302         return isPresent ? Integer.hashCode(value) : 0;
 303     }
 304 
 305     /**
 306      * Returns a non-empty string representation of this {@code OptionalInt}
 307      * suitable for debugging.  The exact presentation format is unspecified and
 308      * may vary between implementations and versions.
 309      *
 310      * @implSpec
 311      * If a value is present the result must include its string representation
 312      * in the result.  Empty and present {@code OptionalInt}s must be
 313      * unambiguously differentiable.
 314      *
 315      * @return the string representation of this instance
 316      */
 317     @Override
 318     public String toString() {
 319         return isPresent
 320                 ? String.format("OptionalInt[%s]", value)
 321                 : "OptionalInt.empty";
 322     }
 323 }