import java.util.HashMap;

import java.util.Map;

public class j8merge {

    public static void main(String[] args) {

        // java 8  , merge() 

        Map<String,Integer> map=new HashMap<>();

        map.put("A", );

        map.put("B", );

        map.put("C", );

        // add new key value ("A",99), if key "A" exist in map then do function  "(X,Y) -> (Y+X)" ,the function return value will replace the oldvalue.

        Integer newValue1 = map.merge("A", , (X,Y) -> (Y+X));

        Integer newValue2 = map.merge("A", , (X,Y) -> Y);

        // add new key value ("D",666), if key "D" not exist in map then insert the key value to map

        Integer newValue3 = map.merge("D", , (X,Y) -> Y);

        Integer newValue4 = map.merge(null, , (X,Y) -> Y);

        Integer newValue5 = map.merge(null, , (X,Y) -> Y);    

        for(String s:map.keySet()){

            System.out.println(s+" : "+map.get(s));

        }

    }

    /*

null : 5555
A : 888
B : 2000
C : 3000
D : 666

*/

}