1 /*
   2  * Copyright (c) 1997, 2016, 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 
  26 
  27 /*
  28  * The Original Code is HAT. The Initial Developer of the
  29  * Original Code is Bill Foote, with contributions from others
  30  * at JavaSoft/Sun.
  31  */
  32 
  33 package jdk.test.lib.hprof.util;
  34 import java.util.*;
  35 
  36 /**
  37  * A singleton utility class that sorts an array of objects.
  38  * <p>
  39  * Use:
  40  * <pre>
  41  *
  42  *  Stuff[] arr = ...;
  43  *  ArraySorter.sort(arr, new Comparer() {
  44  *      public int compare(Object lhs, Object rhs) {
  45  *          return ((String) lhs).compareTo((String) rhs);
  46  *      }
  47  *  });
  48  * </pre>
  49  *
  50  * @author      Bill Foote
  51  */
  52 
  53 public class ArraySorter {
  54 
  55     /**
  56      * Sort the given array, using c for comparison
  57     **/
  58     static public void sort(Object[] arr, Comparer c)  {
  59         quickSort(arr, c, 0, arr.length-1);
  60     }
  61 
  62 
  63     /**
  64      * Sort an array of strings, using String.compareTo()
  65     **/
  66     static public void sortArrayOfStrings(Object[] arr) {
  67         sort(arr, new Comparer() {
  68             public int compare(Object lhs, Object rhs) {
  69                 return ((String) lhs).compareTo((String) rhs);
  70             }
  71         });
  72     }
  73 
  74 
  75     static private void swap(Object[] arr, int a, int b) {
  76         Object tmp = arr[a];
  77         arr[a] = arr[b];
  78         arr[b] = tmp;
  79     }
  80 
  81     //
  82     // Sorts arr between from and to, inclusive.  This is a quick, off-the-top-
  83     // of-my-head quicksort:  I haven't put any thought into optimizing it.
  84     // I _did_ put thought into making sure it's safe (it will always
  85     // terminate).  Worst-case it's O(n^2), but it will usually run in
  86     // in O(n log n).  It's well-behaved if the list is already sorted,
  87     // or nearly so.
  88     //
  89     static private void quickSort(Object[] arr, Comparer c, int from, int to) {
  90         if (to <= from)
  91             return;
  92         int mid = (from + to) / 2;
  93         if (mid != from)
  94             swap(arr, mid, from);
  95         Object pivot = arr[from];   // Simple-minded, but reasonable
  96         int highestBelowPivot = from - 1;
  97         int low = from+1;
  98         int high = to;
  99             // We now move low and high toward each other, maintaining the
 100             // invariants:
 101             //      arr[i] <= pivot    for all i < low
 102             //      arr[i] > pivot     for all i > high
 103             // As long as these invariants hold, and every iteration makes
 104             // progress, we are safe.
 105         while (low <= high) {
 106             int cmp = c.compare(arr[low], pivot);
 107             if (cmp <= 0) {   // arr[low] <= pivot
 108                 if (cmp < 0) {
 109                     highestBelowPivot = low;
 110                 }
 111                 low++;
 112             } else {
 113                 int c2;
 114                 for (;;) {
 115                         // arr[high] > pivot:
 116                     c2 = c.compare(arr[high], pivot);
 117                     if (c2 > 0) {
 118                         high--;
 119                         if (low > high) {
 120                             break;
 121                         }
 122                     } else {
 123                         break;
 124                     }
 125                 }
 126                 // At this point, low is never == high, BTW
 127                 if (low <= high) {
 128                     swap(arr, low, high);
 129                     if (c2 < 0) {
 130                         highestBelowPivot = low;
 131                     }
 132                     low++;
 133                     high--;
 134                 }
 135             }
 136         }
 137         // At this point, low == high+1
 138         // Now we just need to sort from from..highestBelowPivot
 139         // and from high+1..to
 140         if (highestBelowPivot > from) {
 141             // pivot == pivot, so ensure algorithm terminates
 142             swap(arr, from, highestBelowPivot);
 143             quickSort(arr, c, from, highestBelowPivot-1);
 144         }
 145         quickSort(arr, c, high+1, to);
 146     }
 147 }