compareTo 比较器

 

package com.spp.testComparator;

import java.util.Comparator;

public class MyComparator implements Comparator {

    @Override
    public int compare(Object o1, Object o2) {
        if(null==o1||null==o2){
            return -1;
        }
        User u1=(User) o1;
        User u2=(User) o2;
        if (u1.getAge() > u2.getAge()) {  
              return 1; // 第一个大于第二个  
        } else if (u1.getAge() < u2.getAge()) {  
              return -1;// 第一个小于第二个  
        } else {  
              return 0; // 等于  
        }
    }

}

　　Test.java:

package com.spp.testComparator;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

    public class Test {

        /**
         * @param args
         */
        public static void main(String[] args) {
            // 接口比较器比较，是定义在类的外部的，它不会破坏user2本身
            List list = new ArrayList();
            User u1 = new User();
            u1.setName("aaa");
            u1.setAge(10);
            list.add(u1);
            User u2 = new User();
            u2.setName("bbb");
            u2.setAge(30);
            list.add(u2);
            User u3 = new User();
            u3.setName("ccc");
            u3.setAge(20);
            list.add(u3);
            //之前：
            for (int i = 0; i < list.size(); i++) {
                User u = (User) list.get(i);
                System.out.println("之前："+u.getAge());
            }
            
            Collections.sort(list, new MyComparator());
            
            for (int i = 0; i < list.size(); i++) {
                User u = (User) list.get(i);
                System.out.println("之后："+u.getAge());
            }
        }
}

package com.spp.testComparator;

public class User {
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        private String name;
        private int age;
        
}

通过实现Comparator接口，可以实现多种复杂情况的比较