list集合Collections.sort排序的两种用法

注：
本文转载其他人
原文链接：http://gwh-08.iteye.com/blog/1233401/

 

/**
* @author guwh
* @version 创建时间：2011-11-3 上午10:49:36
* 类说明
*/ 
package com.jabberchina.test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class SortTest {
	
	
	
	public static void main(String[] args) {
		List<String> lists = new ArrayList<String>();
		List<A> list = new ArrayList<A>();
		List<B> listB = new ArrayList<B>();
		lists.add("5");
		lists.add("2");
		lists.add("9");
		//lists中的对象String 本身含有compareTo方法，所以可以直接调用sort方法，按自然顺序排序，即升序排序
		Collections.sort(lists);
		
		A aa = new A();
		aa.setName("aa");
		aa.setOrder(1);
		A bb = new A();
		bb.setName("bb");
		bb.setOrder(2);
		list.add(bb);
		list.add(aa);
		//list中的对象A实现Comparable接口
		Collections.sort(list);
		
		B ab = new B();
		ab.setName("ab");
		ab.setOrder("1");
		B ba = new B();
		ba.setName("ba");
		ba.setOrder("2");
		listB.add(ba);
		listB.add(ab);
		//根据Collections.sort重载方法来实现
		Collections.sort(listB,new Comparator<B>(){
			@Override
			public int compare(B b1, B b2) {
				return b1.getOrder().compareTo(b2.getOrder());
			}
			
		});
		
		System.out.println(lists);
		System.out.println(list);
		System.out.println(listB);
		
	}

}

class A implements Comparable<A>{
	private String name;
	private Integer order;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	public Integer getOrder() {
		return order;
	}
	public void setOrder(Integer order) {
		this.order = order;
	}
	@Override
	public String toString() {
		return "name is "+name+" order is "+order;
	}
	@Override
	public int compareTo(A a) {
		return this.order.compareTo(a.getOrder());
	}
	
}

class B{
	private String name;
	private String order;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getOrder() {
		return order;
	}
	public void setOrder(String order) {
		this.order = order;
	}
	@Override
	public String toString() {
		return "name is "+name+" order is "+order;
	}
}

打印的结果为：
&nbsp;[2, 5, 9]
[name is aa order is 1, name is bb order is 2]
[name is ab order is 1, name is ba order is 2]

 

注：如果：return b1.getOrder().compareTo(b2.getOrder()); 改为
return b2.getOrder().compareTo(b1.getOrder());   
那么list中的结果正好相反