Java self - Collections Framework HashMap

Java Collections Framework HashMap

Example. 1: the HashMap value pairs

The data storage mode HashMap - key-value pairs

package collection;
   
import java.util.HashMap;
   
public class TestCollection {
    public static void main(String[] args) {
        HashMap<String,String> dictionary = new HashMap<>();
        dictionary.put("adc", "物理英雄");
        dictionary.put("apc", "魔法英雄");
        dictionary.put("t", "坦克");
         
        System.out.println(dictionary.get("t"));
    }
}

Example 2: key can not be repeated, the value may be repeated

For HashMap, key is unique and can not duplicate.
So, in the same key to a different value is inserted into the Map would cause the old elements are covered, leaving only the last inserted element.
However, the same object can be inserted as a value into the map, as long as the key is not the same as the corresponding

package collection;
  
import java.util.HashMap;
  
import charactor.Hero;
  
public class TestCollection {
    public static void main(String[] args) {
        HashMap<String,Hero> heroMap = new HashMap<String,Hero>();
         
        heroMap.put("gareen", new Hero("gareen1"));
        System.out.println(heroMap);
         
        //key为gareen已经有value了，再以gareen作为key放入数据，会导致原英雄，被覆盖
        //不会增加新的元素到Map中
        heroMap.put("gareen", new Hero("gareen2"));
        System.out.println(heroMap);
         
        //清空map
        heroMap.clear();
        Hero gareen = new Hero("gareen");
         
        //同一个对象可以作为值插入到map中，只要对应的key不一样
        heroMap.put("hero1", gareen);
        heroMap.put("hero2", gareen);
         
        System.out.println(heroMap);
         
    }
}