comparable的使用(用于list)

1. 写一个Person类，继承自Comparable接口，只需重写compareTo（）：

代码语言：javascript复制

package ComparableTest;

public class Person implements Comparable<Person>{
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name=name;
        this.age=age;
    }

    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;
    }
    @Override
    public int compareTo(Person o) {
        return name.compareTo(o.name);
    }
}

1. 写一个Main类，实现main函数：

代码语言：javascript复制

package ComparableTest;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import ComparableTest.Main.AgeAscComparator;

public class Main {


    public static void main(String[] args) {
        ArrayList<Person> list = new ArrayList<Person>();
        list.add(new Person("c", 20));
        list.add(new Person("A", 30));
        list.add(new Person("b", 10));
        list.add(new Person("a", 40));
        print(list,"原始排序：");
        //1. 利用Comparable实现name排序
        Collections.sort(list);  
        print(list,"利用Comparable实现name排序后：");
        //2. 利用Comparator实现age升序
        Collections.sort(list, new AgeAscComparator());
        print(list,"利用Comparator按age升序排序后：");
        //3. 利用Comparator实现age降序
        Collections.sort(list, new AgeDecComparator());
        print(list,"利用Comparator按age降序排序后：");
    }

    //利用Comparator按age升序排序
    public static class AgeAscComparator implements Comparator {
        @Override
        public int compare(Object arg0, Object arg1) {
            Person p0=(Person) arg0;
            Person p1=(Person) arg1;
            return p0.getAge()-p1.getAge();
        }
    }

    //利用Comparator按age降序排序
    public static class AgeDecComparator implements Comparator {
        @Override
        public int compare(Object arg0, Object arg1) {
            Person p0=(Person) arg0;
            Person p1=(Person) arg1;
            return p1.getAge()-p0.getAge();
            }
    }

    public static void print(ArrayList<Person> list,String str){
        System.out.println();
        System.out.print(str);
        for(Person p:list)
            System.out.print(p.getName() ":" p.getAge() "   ");
    }
}

输出结果：

代码语言：javascript复制

原始排序：c:20   A:30   b:10   a:40   
利用Comparable实现name排序后：A:30   a:40   b:10   c:20   
利用Comparator按age升序排序后：b:10   c:20   A:30   a:40   
利用Comparator按age降序排序后：a:40   A:30   c:20   b:10   

如果想实现按name降序排序,只需将Person类中的compareTo中的return改为：

代码语言：javascript复制

@Override
    public int compareTo(Person o) {
        return o.name.compareTo(name);
    }

输出： 利用Comparable实现name降序排序后：c:20 b:10 a:40 A:30

总结： 升序：return name.compareTo(o.name); 降序：return o.name.compareTo(name);

return 函数 继承 接口 排序

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