jdk中提供的快速排序的实现

/*
 * Copyright (c) 1996, 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.
 */

/**
 * Sort: a class that uses the quicksort algorithm to sort an
 *       array of objects.
 *
 * @author Sunita Mani
 */

package sun.misc;

public class Sort {

    private static void swap(Object arr[], int i, int j) {
        Object tmp;

        tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }

    /**
     * quicksort the array of objects.
     *
     * @param arr[] - an array of objects
     * @param left - the start index - from where to begin sorting
     * @param right - the last index.
     * @param comp - an object that implemnts the Compare interface to resolve thecomparison.
     */
    public static void quicksort(Object arr[], int left, int right, Compare comp) {
        int i, last;

        if (left >= right) { /* do nothing if array contains fewer than two */
            return;          /* two elements */
        }
        swap(arr, left, (left+right) / 2);
        last = left;
        for (i = left+1; i <= right; i++) {
            if (comp.doCompare(arr[i], arr[left]) < 0) {
                swap(arr, ++last, i);
            }
        }
        swap(arr, left, last);
        quicksort(arr, left, last-1, comp);
        quicksort(arr, last+1, right, comp);
    }

    public static void quicksort(Object arr[], Compare comp) {
        quicksort(arr, 0, arr.length-1, comp);
    }
}

 

pivot使用的中间元素