EquivalenceComparatorChainBase.java

/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2008, by Barak Naveh and Contributors.
 *
 * This program and the accompanying materials are dual-licensed under
 * either
 *
 * (a) the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation, or (at your option) any
 * later version.
 *
 * or (per the licensee's choosing)
 *
 * (b) the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation.
 */
/* -----------------
 * EquivalenceComparatorChainBase.java
 * -----------------
 * (C) Copyright 2005-2008, by Assaf Lehr and Contributors.
 *
 * Original Author:  Assaf Lehr
 * Contributor(s):   -
 *
 * $Id: EquivalenceComparatorChainBase.java 485 2006-06-26 09:12:14Z perfecthash
 * $
 *
 * Changes
 * -------
 */
package org.jgrapht.experimental.equivalence;

import java.util.*;


/**
 * This class implements comparator chaining.
 *
 * <p>Usage examples:
 * <li> <i>graph-theory, node equivalence:</i> You can create a comparator for
 * the inDegree of a node, another for the total weight of outDegree edges, and
 * a third which checks the business content of the node. You know that the
 * first topological comparators has dozens of different groups, but the
 * buisness comparator has only two, and they are hard to check . The best
 * performance will be gained by:
 *
 * <blockquote><code>
 * <p>EquivalenceComparatorChainBase eqChain = new
 * EquivalenceComparatorChainBase(fastNodesDegreeComparator);
 *
 * <p>eqChain.addComparatorAfter(ABitSlowerEdgeWeightComparator);
 *
 * <p>eqChain.addComparatorAfter(slowestBuisnessContentsComparator);</code>
 * </blockquote>
 *
 * @param <E> the type of the elements in the set
 * @param <C> the type of the context the element is compared against, e.g. a
 * Graph
 *
 * @author Assaf
 * @since Jul 22, 2005
 */
public class EquivalenceComparatorChainBase<E, C>
    implements EquivalenceComparatorChain<E, C>
{
    

    private List<EquivalenceComparator<? super E, ? super C>> chain;

    

    /**
     */
    public EquivalenceComparatorChainBase(
        EquivalenceComparator<E, C> firstComaparator)
    {
        this.chain =
            new LinkedList<EquivalenceComparator<? super E, ? super C>>();
        this.chain.add(firstComaparator);
    }

    

    /* (non-Javadoc)
     * @see
     *
     *
     *
     *
     *
     * org.jgrapht.experimental.equivalence.EquivalenceComparatorChain#addComparatorAfter(org.jgrapht.experimental.equivalence.EquivalenceComparator)
     */
    @SuppressWarnings("unchecked")
    public void appendComparator(EquivalenceComparator comparatorAfter)
    {
        if (comparatorAfter != null) {
            this.chain.add(comparatorAfter);
        }
    }

    /**
     * Implements logical AND between the comparators results. Iterates through
     * the comparators chain until one of them returns false. If none returns
     * false, this method returns true.
     *
     * @see EquivalenceComparator#equivalenceCompare(Object, Object, Object,
     * Object)
     */
    public boolean equivalenceCompare(
        E arg1,
        E arg2,
        C context1,
        C context2)
    {
        for (
            EquivalenceComparator<? super E, ? super C> currentComparator
            : this.chain)
        {
            if (!currentComparator.equivalenceCompare(
                    arg1,
                    arg2,
                    context1,
                    context2))
            {
                return false;
            }
        }
        return true;
    }

    /**
     * Rehashes the concatenation of the results of all single hashcodes.
     *
     * @see EquivalenceComparator#equivalenceHashcode(Object, Object)
     */
    public int equivalenceHashcode(E arg1, C context)
    {
        StringBuffer hashStringBuffer = new StringBuffer();
        for (
            ListIterator<EquivalenceComparator<? super E, ? super C>> iter =
                this.chain.listIterator();
            iter.hasNext();)
        {
            EquivalenceComparator<? super E, ? super C> currentComparator =
                iter.next();
            int currentHashCode =
                currentComparator.equivalenceHashcode(arg1, context);
            hashStringBuffer.append(currentHashCode);

            // add a delimeter only if needed for next
            if (iter.hasNext()) {
                hashStringBuffer.append('+');
            }
        }
        return hashStringBuffer.toString().hashCode();
    }
}

// End EquivalenceComparatorChainBase.java