comparablecomparator.java

Java数据结构开发包

/*
  Copyright (c) 1999, 2000 Brown University, Providence, RI
  
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*/

package jdsl.core.ref;

import java.lang.Comparable;



/** 
 * Implementation of JDSL's Comparator interface in terms of the JDK's
 * Comparable interface.  Compares any two Comparables, regardless of
 * their actual type.
 *
 * @author Mike Boilen (mgb)
 * @author Luca Vismara (lv)
 * @version JDSL 2.1.1 
 */
public class ComparableComparator extends AbstractComparator
  implements jdsl.core.api.Comparator {

  /** 
   * Invokes the <code>compareTo</code> method of <code>x1</code> on
   * <code>x2</code>.
   *
   * @param x1 A <code>Comparable</code> to which <code>x2</code> will
   * be compared.
   * @param x2 An <code>Object</code> which will be compared to
   * <code>x1</code>
   * @exception ClassCastException if <code>x1</code> is
   * <code>null</code> or not a <code>Comparable</code>
   * @see Comparable
   */
  public int compare (Object x1, Object x2) throws ClassCastException {
    if( x1 == null )
      throw new ClassCastException (" asked to compare with null");
    
    //this will generate a ClassCastException if x1 is of the wrong
    //type.
    Comparable comparable = (Comparable)x1;
    
    //This may throw exceptions depending on the implementation of x1.
    return comparable.compareTo( x2 );
  }

  /** 
   * @param o Object you propose to compare with this comparator
   * @return Whether o is a non-null <code>Comparable</code>
   * @see Comparable
   */
  public boolean isComparable (Object o) {
    return ((o != null) && (o instanceof Comparable));
  }

}