// A class for structuring associations that may be compared.// (c) 1998, 2001 duane a. baileypackage structure;/** * A class implementing a comparable key-value pair.  This class associates an  * immutable key with a mutable value.  Useful for many other structures. * Example usage: * <P> * To print out a list of professors sorted by the number of classes * a particular student took from each, we could use the following: * <pre> * public static void main(String[] argv){ *	//initialize a new fib heap *	FibHeap classesTaken = new FibHeap(); * *	//add professors and classes taken to a heap *	classesTaken.add(new {@link #ComparableAssociation(Comparable, Object) ComparableAssociation(new Integer(5), "Andrea")}); *	classesTaken.add(new ComparableAssociation(new Integer(1), "Barbara")); *	classesTaken.add(new ComparableAssociation(new Integer(3), "Bill")); *	classesTaken.add(new ComparableAssociation(new Integer(2), "Duane"));	 *	classesTaken.add(new ComparableAssociation(new Integer(1), "Tom"));	 * *	//print out classes taken *	while(!classesTaken.isEmpty()){ *	    ComparableAssociation p = (ComparableAssociation)classesTaken.remove(); *	    System.out.println(p.{@link #getValue() getValue()} + " is " + p.{@link #getKey() getKey()} + " years old."); *	} * } * </pre>   * @version $Id: ComparableAssociation.java,v 4.0 2000/12/27 20:57:33 bailey Exp bailey $ * @author, 2001 duane a. bailey */public class ComparableAssociation extends Association    implements Comparable{    /**     * Construct an association that can be ordered, from only a key.     * The value is set to null.     *     * @pre key is non-null     * @post constructs comparable association with null value     *      * @param key The (comparable) key.     */    public ComparableAssociation(Comparable key)    {	this(key,null);    }    /**     * Construct a key-value association that can be ordered.     *     * @pre key is non-null     * @post constructs association between a comparable key and a value     *      * @param key The (comparable) key.     * @param value The (possibly comparable) associated value.     */    public ComparableAssociation(Comparable key, Object value)    {	super(key,value);    }    /**     * Determine the order of two comparable associations, based on key.     *     * @pre other is non-null ComparableAssociation     * @post returns integer representing relation between values     *      * @param other The other comparable association.     * @return Value less-than equal to or greater than zero based on comparison     */    public int compareTo(Object other)    {	Assert.pre(other instanceof ComparableAssociation,		   "compareTo expects a ComparableAssociation");	ComparableAssociation that = (ComparableAssociation)other;	Comparable thisKey = (Comparable)this.getKey();	Comparable thatKey = (Comparable)that.getKey();	return thisKey.compareTo(thatKey);    }    /**     * Construct a string representation of the ComparableAssociation.     *     * @post returns string representation     *      * @return The string representing the ComparableAssociation.     */    public String toString()    {	StringBuffer s = new StringBuffer();	s.append("<ComparableAssociation: "+getKey()+"="+getValue()+">");	return s.toString();    }}