1 /*
   2  * Copyright 2009 Sun Microsystems, Inc.  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.  Sun designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  22  * CA 95054 USA or visit www.sun.com if you need additional information or
  23  * have any questions.
  24  */
  25 
  26 package java.util;
  27 
  28 /**
  29  * This class consists of {@code static} utility methods for operating
  30  * on objects.  These utilities include {@code null}-safe or {@code
  31  * null}-tolerant methods for computing the hash code of an object,
  32  * returning a string for an object, and comparing two objects.
  33  *
  34  * @since 1.7
  35  */
  36 public class Objects {
  37     private Objects() {
  38         throw new AssertionError("No java.util.Objects instances for you!");
  39     }
  40 
  41     /**
  42      * Returns {@code true} if the arguments are equal to each other
  43      * and {@code false} otherwise.
  44      * Consequently, if both arguments are {@code null}, {@code true}
  45      * is returned and if exactly one argument is {@code null}, {@code
  46      * false} is returned.  Otherwise, equality is determined by using
  47      * the {@link Object#equals equals} method of the first
  48      * argument.
  49      *
  50      * @return {@code true} if the arguments are equal to each other
  51      * and {@code false} otherwise
  52      * @see Object#equals(Object)
  53      */
  54     public static boolean equals(Object a, Object b) {
  55         return (a == b) || (a != null && a.equals(b));
  56     }
  57 
  58     /**
  59      * Returns the hash code of a non-{@code null} argument and 0 for
  60      * a {@code null} argument.
  61      *
  62      * @return the hash code of a non-{@code null} argument and 0 for
  63      * a {@code null} argument
  64      * @see Object#hashCode
  65      */
  66     public static int hashCode(Object o) {
  67         return o != null ? o.hashCode() : 0;
  68     }
  69 
  70     /**
  71      * Returns the result of calling {@code toString} for a non-{@code
  72      * null} argument and {@code "null"} for a {@code null} argument.
  73      *
  74      * @return the result of calling {@code toString} for a non-{@code
  75      * null} argument and {@code "null"} for a {@code null} argument
  76      * @see Object#toString
  77      * @see String#valueOf(Object)
  78      */
  79     public static String toString(Object o) {
  80         return String.valueOf(o);
  81     }
  82 
  83     /**
  84      * Returns 0 if the arguments are identical and {@code
  85      * c.compare(a, b)} otherwise.
  86      * Consequently, if both arguments are {@code null} 0
  87      * is returned.
  88      *
  89      * <p>Note that if one of the arguments is {@code null}, a {@code
  90      * NullPointerException} may or may not be thrown depending on
  91      * what ordering policy, if any, the {@link Comparator Comparator}
  92      * chooses to have for {@code null} values.
  93      *
  94      * @return 0 if the arguments are identical and {@code
  95      * c.compare(a, b)} otherwise.
  96      * @see Comparable
  97      * @see Comparator
  98      */
  99     public static <T> int compare(T a, T b, Comparator<? super T> c) {
 100         return (a == b) ? 0 :  c.compare(a, b);
 101     }
 102 }