Java---HashMap的增删改查代码

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

/**
 * @author created  by jackie on 2020/4/23
 * @description: map集合的
 */

public class MapDemo {

    @Test
    public  void mapTest(){
        Map<String,String> map = new HashMap<String,String>();

        //添加数据
        map.put("jackie","Guangzhou");
        map.put("lily","Beijing");
        map.put("Ben","Shanghai");

       //查询方法一：使用迭代器打印vaules值
       Iterator<String> values = map.values().iterator();
       while(values.hasNext()){
           System.out.println(values.next()+" ");
      }

        //查询方法二：使用entryset方法得到key-value值
        Set<Map.Entry<String,String>> entrySet = map.entrySet();
        for (Map.Entry<String,String> entry:entrySet){
            System.out.println(entry.getKey()+"-"+entry.getValue());
        }

        //查询方法三：通过key找到vaule
        String vaule = map.get("jackie");
        System.out.println(vaule);

        //查询方法四：不知道key情况下，用map.keySet()取map中的vaule
        for (String key:map.keySet()) {
            String val = map.get(key);
            System.out.println(key + "-"+val);
        }

        //修改value值
        map.replace("jackie","Zhuhai");


        //通过Key值删除记录
        map.remove("jackie");


    }
}