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

时间:2022-06-05 11:12:51

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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/**
* 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());
    }
}
      
      
      
      
     </user>

测试一下:

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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());
        }
    }
}
       
       
       
       
      </user>
      
      
      
      
     </user>

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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/**
* 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:

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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>
        
        
        
        
       ();
        list.add(user2);
        list.add(user1);
         
        Collections.sort(list,new Comparator
        
        
        
        
       <user>
         
         
         
         
        (){
            public int compare(User arg0, User arg1) {
                return arg0.getOrder().compareTo(arg1.getOrder());
            }
        });
        for(User u : list){
            System.out.println(u.getName());
        }
    }
}
        
        
        
        
       </user>
       
       
       
       
      </user>
      
      
      
      
     </user>

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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Collections.sort(list,new Comparator
       
       
       
       
      <user>
        
        
        
        
       (){
            public int compare(User arg0, User arg1) {
 //            第一次比较专业
                int i = arg0.getOrder().compareTo(arg1.getOrder());
//            如果专业相同则进行第二次比较
            if(i==0){
//                第二次比较
                int j=arg0.getXXX().compareTo(arg1.getXXX());
//                如果学制相同则返回按年龄排序
                if(j==0){
                    return arg0.getCCC().compareTo(arg1.getCCC());
                }
                return j;
            }
            return i;
            }
        });
       
       
       
       
      </user>