TreeSet的两种排序方法：自然排序和定义比较器，推荐使用定义比较器方法。

import java.util.*;class treeset {	public static void main(String[] args) 	{		TreeSet t = new TreeSet();//		TreeSet t = new TreeSet(new mycomparator());//第二种方法定义		t.add(new student("a1",18));		t.add(new student("a2",18));		t.add(new student("a1",18));		t.add(new student("a3",16));		t.add(new student("a4",25));		for(Iterator it = t.iterator();it.hasNext();)		{			student s = (student)it.next();			sop(s.getName()+","+s.getAge());		}	}	public static void sop(Object obj)	{		System.out.println(obj);	}}/*自然排序法 定义Comparable接口，覆盖CompareTo方法*/class student implements Comparable{	private String name;	private int age;	student(String name,int age)	{		this.name = name;		this.age = age;	}	public int compareTo(Object obj)	{		if(!(obj instanceof student))			throw new RuntimeException("不是学生");		student s = (student)obj;		if(this.age>s.age)			return 1;		if(this.age==s.age)			return this.name.compareTo(s.name);		return -1;	}	public String getName()	{		return name;	}	public int getAge()	{		return age;	}}/*定义比较器   当两种方法都存在时，以比较器为主。定义一个类，实现Comparator接口，覆盖compare方法*/class mycomparator implements Comparator{	public int compare(Object o1,Object o2)	{		student s1 = (student)o1;		student s2 = (student)o2;		int num = s1.getName().compareTo(s2.getName());		if(num ==0)		{			if(s1.getAge()>s2.getAge())				return 1;			if(s1.getAge()==s2.getAge())				return 0;			return -1;		}		return num;	}}