Comparable使一个class具备不同实例间进行比较的行为。这些对象的集合，可作为Collections.sort或Arrays.sort的参数

Comparator可以看成一种算法的实现，将算法和数据分离。实现Comparator的可以作为Collections.sort或Arrays.sort的参数

都可以多条件排序。类似于order by field1,field2

都是接口

 

 

import java.util.Arrays;import java.util.Comparator;public class UserComparator implements Comparator
     
       {    /**     *     * @param source     * @param target     * @return 负数：升序；0：顺序不变；正数：降序     */    @Override    public int compare(User source, User target) {        int result = source.getAge() - target.getAge();        System.out.println(result);        return result;    }    public static void main(String[] args) {        User[] users = new User[]{
   new User("a", 30), new User("b", 20)};        Arrays.sort(users, new UserComparator());        for (int i = 0; i < users.length; i++) {            User user = users[i];            System.out.println(user.getId() + " " + user.getAge());        }    }}class User {    private String id;    private int age;    public User(String id, int age) {        this.id = id;        this.age = age;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getId() {        return id;    }    public void setId(String id) {        this.id = id;    }}
     

 

 

import java.util.Arrays;public class User implements Comparable
     
       {    private String id;    private int age;    public User(String id, int age) {        this.id = id;        this.age = age;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getId() {        return id;    }    public void setId(String id) {        this.id = id;    }    @Override    public int compareTo(User target) {        int result = this.age - target.getAge();        System.out.println(result);        return result;    }    public static void main(String[] args) {        User[] users = new User[]{
   new User("a", 30), new User("b", 20)};        Arrays.sort(users);        for (int i = 0; i < users.length; i++) {            User user = users[i];            System.out.println(user.getId() + " " + user.getAge());        }    }}
     

 

实例如下：

class Student implements Comparable
     
      {    private String name;    private int age;    private float score;        public Student(String name, int age, float score) {        this.name = name;        this.age = age;        this.score = score;    }        public String toString()    {        return name+"\t\t"+age+"\t\t"+score;    }    @Override    public int compareTo(Student o) {        // TODO Auto-generated method stub        if(this.score>o.score)//score是private的，为什么能够直接调用,这是因为在Student类内部            return -1;//由高到底排序        else if(this.score
      
       o.age)                return 1;//由底到高排序            else if(this.age
      
     

程序运行结果:

sunliu 22 100.0

wangwu 20 99.0

zhangsan 20 90.0

lisi 22 90.0

但是在设计类的时候，往往没有考虑到让类实现Comparable接口，那么我们就需要用到另外的一个比较器接口Comparator。

从上面的实例我们可以发现，compareTo(T o)只有一个参数，而Comparator接口中必须要实现的compare(T o1,T o2)就有两个参数。

package edu.sjtu.ist.comutil;import java.util.Comparator;class Student {    private String name;    private int age;    private float score;        public Student(String name, int age, float score) {        this.name = name;        this.age = age;        this.score = score;    }    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;    }    public float getScore() {        return score;    }    public void setScore(float score) {        this.score = score;    }    public String toString()    {        return name+"\t\t"+age+"\t\t"+score;    }}class StudentComparator implements Comparator
     
      {    @Override    public int compare(Student o1, Student o2) {        // TODO Auto-generated method stub        if(o1.getScore()>o2.getScore())            return -1;        else if(o1.getScore()
      
       o2.getAge())                return 1;            else if(o1.getAge()
      
     

上述程序的运行结果与代码实例1一样。