java List 排序 Collections.sort()

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：

[java] view plain copy

/**

* 根据order对User排序

*/

public class User implements Comparable<User>{

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;

}

public int compareTo(User arg0) {

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

}

} 测试一下：

public class Test{

public static void main(String[] args) {

User user1 = new User();

user1.setName("a");

user1.setOrder(1);

User user2 = new User();

user2.setName("b");

user2.setOrder(2);

List<User> list = new ArrayList<User>();

//此处add user2再add user1

list.add(user2);

list.add(user1);

Collections.sort(list);

for(User u : list){

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

}

}

}


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：

[java] view plain copy

/**

* 根据order对User排序

*/

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

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;

}

}

主类中这样写即可(HastSet——>List——>sort进行排序)：

public class Test {

public static void main(String[] args) {

User user1 = new User();

user1.setName("a");

user1.setPrice(11);

User user2 = new User();

user2.setName("b");

user2.setPrice(2);

Set<User> Hset = new HashSet<User>();

Hset.add(user2);

Hset.add(user1);

List<User> list = new ArrayList<User>();

list.addAll(Hset);

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

public int compare(User arg0, User arg1) {

return arg0.getPrice().compareTo(arg1.getPrice());

}

});

for(User u : list){

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

}

}

输出结果如下：

a
b


默认为升序，将。return arg0.getOrder().compareTo(arg1.getOrder()); 改为：
return arg1.getOrder().compareTo(arg0.getOrder());
就成降序的了。