java对集合进行排序的两种方法

有两种方式可以进行集合排序 ：
1. 为集合中对象的所属类实现了 java.lang.Comparable 接口

对需要排序的person类实现Comparable接口，实现接口的CompareTo方法来定义排序的规则

public class Person implements Comparable{
    private final int id;
    private String name;
    private int age;
   
    public Person(int id,String name,int age){
           this.id = id;
           this.name = name;
           this.age = age;
    }
    public int getId(){
           return id;
    }
    public void setName(String name){
           this.name = name;
    }
    public String getName(){
           return name;  
    }
    public void setAge(int age){
           this.age = age;
    }
    public int getAge(){
           return age;     
    }
    @Override
    public String toString(){
           return "Id: " + id + "/tName: " + name + "/tAge: " + age;
    }   
    @Override
    public int compareTo(Object o){      // 实现 Comparable 接口的抽象方法，定义排序规则
           Person p = (Person)o;
           return this.id - p.id;                      // 升序排列，反之降序
    }
    @Override
    public boolean equals(Object o){     //equals
           boolean flag = false;
           if(o instanceof Person){
                  if(this.id == ((Person)o).id)
                         flag = true;
           }
           return false;          
    }    
 
  
}

测试类

import java.util.TreeSet;
import java.util.Iterator;
 
public class TestComparable{
       public static void main(String[] args) {
              TreeSet ts = new TreeSet();
              ts.add(new Person(1003," 张三 ",15));
              ts.add(new Person(1008," 李四 ",25));
              ts.add(new Person(1015," 王五 ",73));
              ts.add(new Person(1001," 赵六 ",49));
 
              Iterator it = ts.iterator();
              while(it.hasNext()){
                     Person employee = (Person)it.next();
                     System.out.println(employee);     
              }
       }
}

2. 为集合指定比较器 java.lang.Comparator 的实现类
需要排序的类

//需要排序的类的对象
public class Person{
    private final int id;
    private String name;
    private int age;
   
    public Person(int id,String name,int age){
           this.id = id;
           this.name = name;
           this.age = age;
    }
    public int getId(){
           return id;
    }
    public void setName(String name){
           this.name = name;
    }
    public String getName(){
           return name; 
    }
    public void setAge(int age){
           this.age = age;
    }
    public int getAge(){
           return age; 
    }
    @Override
    public String toString(){
           return "Id: " + id + "/tName: " + name + "/tAge: " + age;
    } 
}
//创建person类的比较器
package ClassTest;

import java.util.Comparator;
public class PersonComparetor implements Comparator<Person>{

    public int compare(Person o1, Person o2) {
       
// return o1.getId()-o2.getId(); //升序
        return o2.getId()-o1.getId(); //降序
    }
}
//测试类
public class TestComparable {
    public static void main(String[] args) {
        List<Person> ts=new ArrayList<Person>();
        ts.add(new Person(1003," 张三 ",15));
        ts.add(new Person(1008," 李四 ",25));
        ts.add(new Person(1015," 王五 ",73));
        ts.add(new Person(1001," 赵六 ",49));
        PersonComparetor pc=new PersonComparetor();
        Collections.sort(ts, pc);
        for(Person p:ts){
            System.out.println(p);
        }
 }
}