ArraySorter.java revision 2224:2a8815d86b93 
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
33package jdk.test.lib.hprof.util;
34import 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
53public 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}
148