org.primordion.xholon.util.XholonCollections.java Source code

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Here is the source code for org.primordion.xholon.util.XholonCollections.java

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/* Xholon Runtime Framework - executes event-driven & dynamic applications
 * Copyright (C) 2013 Ken Webb
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1
 * of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
 */

package org.primordion.xholon.util;

import com.google.gwt.user.client.Random;
import java.util.Collections;
import java.util.List;

/**
 * This Xholon class implements the shuffle(java.util.List<?>) method which is missing from the
 * GWT implementation of java.util.Collections .
 * @author <a href="mailto:ken@primordion.com">Ken Webb</a>
 * @see <a href="http://www.primordion.com/Xholon">Xholon Project website</a>
 * @since 0.9.0 (Created on August 25, 2013)
 */
public class XholonCollections {

    /*public static void swap(List<?> list, int idx1, int idx2) {
      Object o1 = list.get(idx1);
      list.set(idx1, list.get(idx2));
      list.set(idx2, o1);
    }*/

    /**
     * Randomly permutes the specified list using a default source of randomness.
     * All permutations occur with approximately equal likelihood.
     * This implementation traverses the list backwards, from the last element up to the second,
     * repeatedly swapping a randomly selected element into the "current position".
     * Elements are randomly selected from the portion of the list that runs from the first
     * element to the current position, inclusive.
     * This method runs in linear time.
     * @param list - the list to be shuffled.
     * The performance will degrade if the list does not implement RandomAccess.
     * ArrayList and Vector do implement RandomAccess.
     */
    public static void shuffle(List<?> list) {
        for (int i = list.size(); i > 1; i--) {
            Collections.swap(list, i - 1, Random.nextInt(i));
        }
    }

}