quicksort algorithm implementation java code- array sorting

/*
 * Copyright (c) 1995-1997 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies. Please refer to the file "copyright.html"
 * for further important copyright and licensing information.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 */
/*
 * @(#)QSortAlgorithm.java	1.6f 95/01/31 James Gosling
 *
 * Copyright (c) 1994 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies. Please refer to the file "copyright.html"
 * for further important copyright and licensing information.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 */

/**
 * A quick sort demonstration algorithm
 * SortAlgorithm.java, Thu Oct 27 10:32:35 1994
 *
 * @author James Gosling
 * @version 	1.6f, 31 Jan 1995
 */
class QSortAlgorithm extends SortAlgorithm {
    void sort(int[] a, int lo0, int hi0) throws Exception {
	int lo = lo0;
	int hi = hi0;
	pause(lo, hi);
	if (lo >= hi) {
	    return;
	}
	int mid = a[(lo + hi) / 2];
	while (lo < hi) {
	    while (lo<hi && a[lo] < mid) {
		lo++;
	    }
	    while (lo<hi && a[hi] > mid) {
		hi--;
	    }
	    if (lo < hi) {
		int T = a[lo];
		a[lo] = a[hi];
		a[hi] = T;
		pause();
	    }
	}
	if (hi < lo) {
	    int T = hi;
	    hi = lo;
	    lo = T;
	}
	sort(a, lo0, lo);
	sort(a, lo == lo0 ? lo+1 : lo, hi0);
    }

    void sort(int[] a) throws Exception {
	sort(a, 0, a.length-1);
    }
}

class SortAlgorithm {
    /**
     * The sort item.
     */
    private SortItem parent;

    /**
     * When true stop sorting.
     */
    protected boolean stopRequested = false;

    /**
     * Set the parent.
     */
    public void setParent(SortItem p) {
	parent = p;
    }

    /**
     * Pause for a while.
     */
    protected void pause() throws Exception {
	if (stopRequested) {
	    throw new Exception("Sort Algorithm");
	}
	parent.pause(parent.h1, parent.h2);
    }

    /**
     * Pause for a while and mark item 1.
     */
    protected void pause(int H1) throws Exception {
	if (stopRequested) {
	    throw new Exception("Sort Algorithm");
	}
	parent.pause(H1, parent.h2);
    }

    /**
     * Pause for a while and mark item 1 & 2.
     */
    protected void pause(int H1, int H2) throws Exception {
	if (stopRequested) {
	    throw new Exception("Sort Algorithm");
	}
	parent.pause(H1, H2);
    }

    /**
     * Stop sorting.
     */
    public void stop() {
	stopRequested = true;
    }

    /**
     * Initialize
     */
    public void init() {
	stopRequested = false;
    }

    /**
     * This method will be called to
     * sort an array of integers.
     */
    void sort(int[] a) throws Exception {
    }
}