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Java example source code file (ArraySorter.java)

This example Java source code file (ArraySorter.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraysorter, comparer, object, simple-minded, string, util

The ArraySorter.java Java example source code

/*
 * Copyright (c) 1997, 2008, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */


/*
 * The Original Code is HAT. The Initial Developer of the
 * Original Code is Bill Foote, with contributions from others
 * at JavaSoft/Sun.
 */

package com.sun.tools.hat.internal.util;
import java.util.*;

/**
 * A singleton utility class that sorts an array of objects.
 * <p>
 * Use:
 * <pre>
 *
 *  Stuff[] arr = ...;
 *  ArraySorter.sort(arr, new Comparer() {
 *      public int compare(Object lhs, Object rhs) {
 *          return ((String) lhs).compareTo((String) rhs);
 *      }
 *  });
 * </pre>
 *
 * @author      Bill Foote
 */

public class ArraySorter {

    /**
     * Sort the given array, using c for comparison
    **/
    static public void sort(Object[] arr, Comparer c)  {
        quickSort(arr, c, 0, arr.length-1);
    }


    /**
     * Sort an array of strings, using String.compareTo()
    **/
    static public void sortArrayOfStrings(Object[] arr) {
        sort(arr, new Comparer() {
            public int compare(Object lhs, Object rhs) {
                return ((String) lhs).compareTo((String) rhs);
            }
        });
    }


    static private void swap(Object[] arr, int a, int b) {
        Object tmp = arr[a];
        arr[a] = arr[b];
        arr[b] = tmp;
    }

    //
    // Sorts arr between from and to, inclusive.  This is a quick, off-the-top-
    // of-my-head quicksort:  I haven't put any thought into optimizing it.
    // I _did_ put thought into making sure it's safe (it will always
    // terminate).  Worst-case it's O(n^2), but it will usually run in
    // in O(n log n).  It's well-behaved if the list is already sorted,
    // or nearly so.
    //
    static private void quickSort(Object[] arr, Comparer c, int from, int to) {
        if (to <= from)
            return;
        int mid = (from + to) / 2;
        if (mid != from)
            swap(arr, mid, from);
        Object pivot = arr[from];   // Simple-minded, but reasonable
        int highestBelowPivot = from - 1;
        int low = from+1;
        int high = to;
            // We now move low and high toward each other, maintaining the
            // invariants:
            //      arr[i] <= pivot    for all i < low
            //      arr[i] > pivot     for all i > high
            // As long as these invariants hold, and every iteration makes
            // progress, we are safe.
        while (low <= high) {
            int cmp = c.compare(arr[low], pivot);
            if (cmp <= 0) {   // arr[low] <= pivot
                if (cmp < 0) {
                    highestBelowPivot = low;
                }
                low++;
            } else {
                int c2;
                for (;;) {
                        // arr[high] > pivot:
                    c2 = c.compare(arr[high], pivot);
                    if (c2 > 0) {
                        high--;
                        if (low > high) {
                            break;
                        }
                    } else {
                        break;
                    }
                }
                // At this point, low is never == high, BTW
                if (low <= high) {
                    swap(arr, low, high);
                    if (c2 < 0) {
                        highestBelowPivot = low;
                    }
                    low++;
                    high--;
                }
            }
        }
        // At this point, low == high+1
        // Now we just need to sort from from..highestBelowPivot
        // and from high+1..to
        if (highestBelowPivot > from) {
            // pivot == pivot, so ensure algorithm terminates
            swap(arr, from, highestBelowPivot);
            quickSort(arr, c, from, highestBelowPivot-1);
        }
        quickSort(arr, c, high+1, to);
    }
}

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