用Java集合中的Collections.sort方法对list排序的两种方法

用Collections.sort方法对list排序有两种方法

第一种是list中的对象实现Comparable接口，如下：

 

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01	<strong>/**

02	* 根据order对User排序

03

*/

04	public class User implements Comparable{

05	private String name;

06	private Integer order;

07	public String getName() {

08	return name;

09

}

10	public void setName(String name) {

11	this.name = name;

12

}

13	public Integer getOrder() {

14	return order;

15

}

16	public void setOrder(Integer order) {

17	this.order = order;

18

}

19	public int compareTo(User arg0) {

20	return this.getOrder().compareTo(arg0.getOrder());

21

}

22

}

23

</strong>

 

 

测试一下：

 

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01	<strong>public class Test{

02

03	public static void main(String[] args) {

04	User user1 = new User();

05	user1.setName("a");

06	user1.setOrder(1);

07	User user2 = new User();

08	user2.setName("b");

09	user2.setOrder(2);

10	List list = new ArrayList();

11	//此处add user2再add user1

12	list.add(user2);

13	list.add(user1);

14	Collections.sort(list);

15	for(User u : list){

16	System.out.println(u.getName());

17

}

18

}

19	}</strong>

输出结果如下
a
b 

 

 

第二种方法是根据Collections.sort重载方法来实现，例如：

 

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01	<strong>/**

02	* 根据order对User排序

03

*/

04	public class User { //此处无需实现Comparable接口

05	private String name;

06	private Integer order;

07	public String getName() {

08	return name;

09

}

10	public void setName(String name) {

11	this.name = name;

12

}

13	public Integer getOrder() {

14	return order;

15

}

16	public void setOrder(Integer order) {

17	this.order = order;

18

}

19	}</strong>

主类中这样写即可：

 

 

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01	<strong>public class Test{

02	public static void main(String[] args) {

03	User user1 = new User();

04	user1.setName("a");

05	user1.setOrder(1);

06	User user2 = new User();

07	user2.setName("b");

08	user2.setOrder(2);

09	List list = new ArrayList();

10	list.add(user2);

11	list.add(user1);

12

13	Collections.sort(list,new Comparator(){

14	public int compare(User arg0, User arg1) {

15	return arg0.getOrder().compareTo(arg1.getOrder());

16

}

17

});

18	for(User u : list){

19	System.out.println(u.getName());

20

}

21

}

22

}

23

</strong>

 

 

输出结果如下
a
b
前者代码结构简单，但是只能根据固定的属性排序，后者灵活，可以临时指定排序项，但是代码不够简洁

多字段的场合： 

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01	<strong>Collections.sort(list,new Comparator(){

02	public int compare(User arg0, User arg1) {

03	//            第一次比较专业

04	int i = arg0.getOrder().compareTo(arg1.getOrder());

05

06	//            如果专业相同则进行第二次比较

07

if(i==0){

08	//                第二次比较

09	int j=arg0.getXXX().compareTo(arg1.getXXX());

10	//                如果学制相同则返回按年龄排序

11

if(j==0){

12	return arg0.getCCC().compareTo(arg1.getCCC());

13

}

14

return j;

15

}

16

return i;

17

}

18

});

19

20

</strong>