naturalcomparator.java

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// A comparator that implements the natural ordering.
// (c) 2001 duane a. bailey

package structure;

import java.util.Comparator;

/**
 * Implementation of the {@link java.util.Comparator} interface that
 * provides a {@link #compare} method that compares two objects using those
 * objects default compareTo methods.
 *  
 * <P>
 * Example usage:
 * <P>
 * To print out the equality relationship between two randomly generated integers
 * we could use the following:
 * <pre>
 * public static void main(String[] argv){
 *     Random  rand = new Random();
 *     Comparator c = new {@link #NaturalComparator()};
 *      
 *     //generate two random Integers
 *     Integer a = new Integer(rand.nextInt(100));
 *     Integer b = new Integer(rand.nextInt(100));
 *      
 *     //print out the proper equality relationship between these integers
 *     if(c.{@link #compare(Object,Object) compare(a,b)} > 0) System.out.println("A:" + a + " > B:" + b);
 *     else if (c.{@link #compare(Object,Object) compare(a,b) < 0) System.out.println("A:" + a + " < B:" + b);
 *     else System.out.println("A:" + a + " = B:" + b);
 * }
 *
 * </pre>
 * @author, 2001 duane a. bailey
 */
public class NaturalComparator implements Comparator
{
    /**
     * Compare two values, a and b.  Simply calls the default
     * compareTo method for a on b.
     * @param a object performing the compare
     * @param b the object being compared
     * @pre a, b non-null, and b is same type as a
     * @post returns value <, ==, > 0 if a <, ==, > b
     * @return value <, ==, > 0 if a <, ==, > b using a.compareTo
     */
    public int compare(Object a, Object b)
    {
	return ((Comparable)a).compareTo(b);
    }

    /**
     * Returns true if the other object is a NaturalComparator.
     * @param b a possible NaturalComparator
     * @post returns true if b is a NaturalComparator
     * @return true if b is a NaturalComparator
     */
    public boolean equals(Object b)
    {
	return (b != null) && (b instanceof NaturalComparator);
    }
}