Map, HashMap, and MapHashMap

Map, HashMap, and MapHashMap

By querying the JDK help documentation, we can learn the description and method of Map.

Import java. util. map; import java. util. hashMap; class Test {public static void main (String args []) {// The first String is the key type, and the second String is the value type HashMap <String, string> hm = new HashMap <String, String> (); // converts the Map type to Map <String, String> map = hm; map. put ("1", "a"); // call the put method and enter a key-value pair to map the data. put ("2", "B"); map. put ("3", "c"); map. put ("4", "d"); map. put ("4", "f"); System. out. println (map. size (); // print the number of key pairs in the map String s = map. get ("4"); // obtain the value System based on the key. out. println (s );}}

When the same key value is added to the Map, the original value will be overwritten.