package exercise;

public class Demo1 {
    public static void main(String[] args) {
        //可变参数
        //方法形参的个数是可以发生变化的
        //格式：属性类型...名字
        //int...args

        int sum = getSum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        System.out.println(sum);
    }

    //底层：可变参数底层就是一个数组
    public static int getSum(int... number) {
        int sum = 0;
        for (int i : number) {
            sum += i;
        }
        return sum;
    }
}

细节：
1.在方法的形参中最多只能写一个可变参数
2.在方法的形参中，如果除了可变参数以外，还有其他的形参，那么可变参数要写在最后

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package exercise;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Random;

public class Demo3 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        Collections.addAll(list, "张三", "李四", "王五");
        /*
            方法一：
            Random r = new Random();
            int i = r.nextInt(list.size());
            System.out.println(list.get(i));
         */

        //方法二：
        Collections.shuffle(list);
        String s = list.get(0);
        System.out.println(s);
    }
}

package exercise;


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

public class Demo4 {
    public static void main(String[] args) {
        /*
            1.创建一个整数数组（1：男生  0：女生），用来判断概率
            2.分别用两个集合来存储男生和女生
            3.将上述集合打乱
            4.用整数数组得到的结果来输出  男生\女集合打乱后的第0个元素
         */
        ArrayList<Integer> list = new ArrayList<>();
        Collections.addAll(list, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0);
        Collections.shuffle(list);
        System.out.println(list.get(0));

        ArrayList<String> boyList = new ArrayList<>();
        ArrayList<String> girlList = new ArrayList<>();
        Collections.addAll(boyList, "男1", "男2", "男3");
        Collections.addAll(girlList, "女1", "女2", "女3");

        Collections.shuffle(boyList);
        Collections.shuffle(girlList);
        if (list.get(0) == 1) {
            System.out.println(boyList.get(0));
        } else {
            System.out.println(girlList.get(0));
        }

    }
}

shift+F6:批量改名

package exercise;

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

public class Demo5 {
    public static void main(String[] args) {
        ArrayList<String> list1 = new ArrayList<>();
        Collections.addAll(list1, "张三", "李四", "王五", "赵六");
        ArrayList<String> list2 = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            System.out.println("============第" + i + "轮================");
            Collections.shuffle(list1);
            int count = list1.size();
            for (int j = 0; j < count; j++) {
                String remove = list1.remove(0);
                list2.add(remove);
                System.out.println(remove);
            }
            list1.addAll(list2);
            list2.clear();
        }
    }
}

package exercise;

import java.util.*;

public class Demo6 {
    public static void main(String[] args) {
        HashMap<String, ArrayList<String>> hm = new HashMap<>();
        ArrayList<String> list1 = new ArrayList<>();
        Collections.addAll(list1, "桂林", "柳州", "南宁");
        ArrayList<String> list2 = new ArrayList<>();
        Collections.addAll(list2, "苏州", "无锡", "南京");
        ArrayList<String> list3 = new ArrayList<>();
        Collections.addAll(list3, "哈尔滨", "大庆", "齐齐哈尔");
        hm.put("广西", list1);
        hm.put("江苏", list2);
        hm.put("黑龙江", list3);

        Set<Map.Entry<String, ArrayList<String>>> entries = hm.entrySet();
        for (Map.Entry<String, ArrayList<String>> entry : entries) {
            String key = entry.getKey();
            ArrayList<String> value = entry.getValue();
            StringJoiner sj = new StringJoiner(",", "", "");
            for (String s : value) {
                sj.add(s);
            }
            System.out.println(key + " = " + sj);
        }
    }
}