demo

package edu.xcdq.set;

import com.sun.org.apache.xerces.internal.impl.xs.models.XSCMUniOp;
import jdk.nashorn.internal.parser.JSONParser;

import java.util.HashSet;

/**
 * @author yuhuicun
 * @date 2021/5/8 9:17
 */
public class HashSetdemo {
    public static void main(String[] args) {
        HashSet<String> set = new HashSet<>();
        set.add("111");
        set.add("222");
        set.add("333");
        set.add("小明");
        set.add("小华");
        set.add("aaa");
        set.add("bbb");
        set.add("xxx");
        System.out.println(set);
        set.add("xxx");
        System.out.println(set);
        int size = set.size();
        boolean empty = set.isEmpty();
        System.out.println(set.parallelStream());
        System.out.println(set);




    }
}

import java.util.HashMap;
import java.util.Map;

/**
 * @author yuhuicun
 * @date 2021/5/8 10:07
 */
public class HashMapDemo {
    public static void main(String[] args) {
        HashMap<String,String> map = new HashMap<>();
        map.put("henan","河南");//  entry  实例
        map.put("hebei","河北");
        map.put("hubei","湖北");
        map.put("hubei","湖北1");//键重复会覆盖掉原有的值
        /*map.put("null","空");
        map.put(null,"空2");
        map.put(null,null);*/
        System.out.println(map);

        for (Map.Entry<String,String>m:map.entrySet()){
            System.out.println(m);

        }
        for (String k : map.keySet()){
            System.out.println(k+"="+map.get(k));
        }
        for (String v : map.values()){
            System.out.println(v);
        }













    }
}