TreeSet实现了SortedSet接口

package iotest;

import java.util.SortedSet;

import java.util.TreeSet;

public class sset {

public static void main(String args[]){

SortedSet<String> alls=new TreeSet<String>();

alls.add("A");

alls.add("M");

alls.add("D");

alls.add("F");

alls.add("F");

System.out.println(alls);

System.out.println(alls.first());

System.out.println(alls.last());

System.out.println(alls.headSet("F"));

System.out.println(alls.tailSet("D"));

System.out.println(alls.subSet("D", "F"));

}

}