Collections工具類中的sort方法有兩種形式：

(1) sort(List<T> list)
(2) sort(List<T> list, Comparator<? super T> c)

第一種方法中List型別的物件必須實現Comparable介面,此外，List中的元素必須可比較。
我們先定義類

package com.dongye.sort;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * @author dongyewujiu
 * @date 19-1-9
 * @description
 */
public class Person implements Comparable {

    private String name;
    private int 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;
    }

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

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @Override
    public int compareTo(Object o) {
        Person person = (Person) o;
        if(this.getAge()>person.getAge()){
            return 1;
        }else if(this.getAge()<person.getAge()){
            return -1;
        }else{
            return 0;
        }
    }
}
 

main方法進行sort方法的呼叫：

 public static void main(String[] args) {
        Person person1 = new Person("德瑪",19);
        Person person2 = new Person("索拉卡",16);
        Person person3 = new Person("妖姬",17);
        List<Person> list = new ArrayList<>();
        list.add(person1);
        list.add(person2);
        list.add(person3);
        Collections.sort(list);
        for (Person p:list){
            System.out.println(p.toString());
        }
    }
 

第二種方法的使用事先無需在自定義物件內部實現排序Comparable介面， 可以在外部實現排序介面Comparator :

public static void main(String[] args) {
        Person person1 = new Person("德瑪",19);
        Person person2 = new Person("索拉卡",16);
        Person person3 = new Person("妖姬",17);
        List<Person> list = new ArrayList<>();
        list.add(person1);
        list.add(person2);
        list.add(person3);
        Collections.sort(list, new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {
                if (o1.getAge() > o2.getAge()) {
                    return 1;
                } else if (o1.getAge() < o2.getAge()) {
                    return -1;
                } else {
                    return 0;
                }
            }
        });        
        for (Person p:list){
            System.out.println(p.toString());
        }
    }