Collections集合工具类

import java.util.*;


public class CollectionsDemo {
    public static void main(String[] args) {
        demo1();
        demo2();
    }

    private static void demo2() {
        ArrayList<String> coll = new ArrayList<String>();
        Collections.addAll(coll, "只1", "sd2", "ad3", "s4");
        //打乱 list集合中元素的位置
        Collections.shuffle(coll);
        System.out.println(coll);
    }

    private static void demo1() {
        HashSet<String> h = new HashSet<>();
        // 往集合中添加一些元素
        Collections.addAll(h, "只", "sd", "ad", "s");
        System.out.println(h);//[sd, ad, s, 只]
    }
}