TreeSet() 类逆向排序(实现compare()方法以便按正常顺序的逆向进行操作)。

/*

仔细观察实现Comparator并覆盖compare()方法的MyComp类（覆盖equals方法既不是必须的，也不是常用的）。在compare()方法内部，String方法compareTo()比较两个字符串。然而由strB-----不是strA------调用compareTo()方法，这导致比较的结果被逆向。

*/

//Use a custom comparator
import java.util.*;
//A reverse comparator for strings.
class MyComp implements Comparator{
public int compare(Object a,Object b){
String strA,strB;
strA = (String)a;
strB = (String)b;

//reverse the comparison
return strB.compareTo(strA);
}
//no need to override equals
}
public class CompDemo{
public static void main(String[] args)
{
//Create a tree set.
TreeSet ts = new TreeSet(new MyComp());

//Ade elements to the tree set
ts.add("C");
ts.add("F");
ts.add("A");
ts.add("B");
ts.add("D");

//Get an iterator
Iterator i = ts.iterator();

//Display elements
while(i.hasNext()){
Object element = i.next();
System.out.println(element + " ");
}
System.out.println();
}
}