1 /*

     2  * Copyright (c) 1997, 2008, 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 com.sun.tools.hat.internal.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 }