1 /*
   2  * Copyright (c) 2017, 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.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
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  41 package jdk.internal.vm.compiler.collections;
  42 
  43 import java.util.Objects;
  44 
  45 /**
  46  * Utility class representing a pair of values.
  47  *
  48  * @since 1.0
  49  */
  50 public final class Pair<L, R> {
  51 
  52     private static final Pair<Object, Object> EMPTY = new Pair<>(null, null);
  53 
  54     private final L left;
  55     private final R right;
  56 
  57     /**
  58      * Returns an empty pair.
  59      *
  60      * @since 1.0
  61      */
  62     @SuppressWarnings("unchecked")
  63     public static <L, R> Pair<L, R> empty() {
  64         return (Pair<L, R>) EMPTY;
  65     }
  66 
  67     /**
  68      * Constructs a pair with its left value being {@code left}, or returns an empty pair if
  69      * {@code left} is null.
  70      *
  71      * @return the constructed pair or an empty pair if {@code left} is null.
  72      * @since 1.0
  73      */
  74     public static <L, R> Pair<L, R> createLeft(L left) {
  75         if (left == null) {
  76             return empty();
  77         } else {
  78             return new Pair<>(left, null);
  79         }
  80     }
  81 
  82     /**
  83      * Constructs a pair with its right value being {@code right}, or returns an empty pair if
  84      * {@code right} is null.
  85      *
  86      * @return the constructed pair or an empty pair if {@code right} is null.
  87      * @since 1.0
  88      */
  89     public static <L, R> Pair<L, R> createRight(R right) {
  90         if (right == null) {
  91             return empty();
  92         } else {
  93             return new Pair<>(null, right);
  94         }
  95     }
  96 
  97     /**
  98      * Constructs a pair with its left value being {@code left}, and its right value being
  99      * {@code right}, or returns an empty pair if both inputs are null.
 100      *
 101      * @return the constructed pair or an empty pair if both inputs are null.
 102      * @since 1.0
 103      */
 104     public static <L, R> Pair<L, R> create(L left, R right) {
 105         if (right == null && left == null) {
 106             return empty();
 107         } else {
 108             return new Pair<>(left, right);
 109         }
 110     }
 111 
 112     private Pair(L left, R right) {
 113         this.left = left;
 114         this.right = right;
 115     }
 116 
 117     /**
 118      * Returns the left value of this pair.
 119      *
 120      * @since 1.0
 121      */
 122     public L getLeft() {
 123         return left;
 124     }
 125 
 126     /**
 127      * Returns the right value of this pair.
 128      *
 129      * @since 1.0
 130      */
 131     public R getRight() {
 132         return right;
 133     }
 134 
 135     /**
 136      * {@inheritDoc}
 137      *
 138      * @since 1.0
 139      */
 140     @Override
 141     public int hashCode() {
 142         return Objects.hashCode(left) + 31 * Objects.hashCode(right);
 143     }
 144 
 145     /**
 146      * {@inheritDoc}
 147      *
 148      * @since 1.0
 149      */
 150     @SuppressWarnings("unchecked")
 151     @Override
 152     public boolean equals(Object obj) {
 153         if (obj == this) {
 154             return true;
 155         }
 156 
 157         if (obj instanceof Pair) {
 158             Pair<L, R> pair = (Pair<L, R>) obj;
 159             return Objects.equals(left, pair.left) && Objects.equals(right, pair.right);
 160         }
 161 
 162         return false;
 163     }
 164 
 165     /**
 166      * {@inheritDoc}
 167      *
 168      * @since 1.0
 169      */
 170     @Override
 171     public String toString() {
 172         return String.format("(%s, %s)", left, right);
 173     }
 174 }