Collections集合工具类，Comparator重写比较方法

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
/**
 * Collections操作集合, 集合工具类
 *Collections.addAll(list,"a","b","c") 添加多个元素
 *Collections.shuffle(list)     打乱元素
 *Collection.sort(list)         默认为升序排序(从小到大)
 * 被排序的集合中的数据类必须重写过Comparable的方法,int,String自带了,
 * 其他类需要自己写
 * 通过自己写的方式比较,重写comparator方法 new Comparator()
 */
public class collections {
     
    public static void main(String[] args) {
     
        ArrayList<String> list = new ArrayList<>();
        //单个添加
        list.add("c");
        list.add("s");
        list.add("b");
        list.add("z");
        /**
         * 添加
         */
        Collections.addAll(list,"a","b","c");
        System.out.println("使用Collection.add 的添加方式\n"+list);
        System.out.println();

        /**
         * 打乱
         */
        Collections.shuffle(list);
        System.out.println("Collections.shuffle 打乱集合 \n"+list);
        System.out.println();

        /**
         * 排序
         */
        Collections.sort(list);
        System.out.println("使用java自带的排序 \n"+list);
        System.out.println();

        /**
         * 对自定义的Comparable比较方法排序
         * 重写比较规则 compareTo
         */
        ArrayList<Person1> list1 = new ArrayList<>();
        list1.add(new Person1("张三",20));
        list1.add(new Person1("李四",19));
        list1.add(new Person1("王五",21));
        Collections.sort(list1);  //通过年龄的比较
        System.out.println("重写compareTo 比较年龄排序\n"+list1);
        System.out.println();

        /**
         * Comparator : 找第三方的裁判,比较两个
         */
        ArrayList<Integer> list2 = new ArrayList<>();
        Collections.addAll(list2,1,3,5,6,8);
        System.out.println(list2);
        Collections.sort(list2, new Comparator<Integer>() {
     
            @Override       //重写Comparator
            public int compare(Integer o1, Integer o2) {
     
                return o2-o1;
            }
        });
        System.out.println("comparator \n"+list2);
        System.out.println();

        /**
         *Comparator , 用自定义的类型,重写comparator
         *
         */
        ArrayList<student> students = new ArrayList<>();
        Collections.addAll(students,new student("迪丽热巴",20),
                new student("古力娜扎",18),new student("杨幂",25));
        Collections.sort(students, new Comparator<student>() {
     
            @Override
            public int compare(student o1, student o2) {
     
                return o1.getAge()-o2.getAge();
            }
        });
        System.out.println("学生类\n"+students);
        System.out.println();
    }
}
class student{
     
    private String name;
    private int age;

    public String getName() {
     
        return name;
    }

    public void setName(String name) {
     
        this.name = name;
    }

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

    public int getAge() {
     
        return age;
    }

    public void setAge(int age) {
     
        this.age = age;
    }

    public student() {
     
    }

    public student(String name, int age) {
     
        this.name = name;
        this.age = age;
    }
}
class Person1 implements Comparable<Person1>{
     
    private String name;
    private int age;

    @Override
    public String toString() {
     
        return "Person1{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public Person1() {
     
    }

    public Person1(String name, int age) {
     
        this.name = name;
        this.age = age;
    }

    public int getAge() {
     
        return age;
    }

    public void setAge(int age) {
     
        this.age = age;
    }

    public String getName() {
     
        return name;
    }

    public void setName(String name) {
     
        this.name = name;
    }

    @Override
    public int compareTo(Person1 o) {
     
        // this.getAge() - o.getAge() 升序
        return this.getAge() - o.getAge();
        // o.getAge() - this.getAge()
    }
}