java中的容器排序，需要类实现Comparable接口， 同时重写该接口的compareTo( )方法。该接口只有这一种方法，当前面类的某个属性值大于后者，返回正值，等于则返回0，小于则返回负值。

import java.util.*;

class Student implements Comparable
{
	String name;
	int id;
	
	public Student()
	{
		
	}
	
	public Student(String name,int id)
	{
		this.name=name;
		this.id=id;
	}
	
	public String toString()
	{
		return name+" "+id;
	}
	
	public int compareTo(Object ob)
	{
		Student st=(Student)ob;
		if(this.id==st.id)
			return 0;
		else if(this.id>st.id)
			return 1;
		else 
			return -1;
	}
}

public class TestJava
{
	public static void main(String[] args)
	{
		ArrayList al=new ArrayList();
		al.add(new Student("zhang",1001));
		al.add(new Student("li",1008));
		al.add(new Student("liu",1006));
		al.add(new Student("xu",1002));
		System.out.println(al);
		Collections.sort(al);
		System.out.println(al);
	}
}