how to add two values together is they are the same in java map code example

Example: how to add two map values in java

//map 1
HashMap<Integer, String> map1 = new HashMap<>();
 
map1.put(1, "A");
map1.put(2, "B");
map1.put(3, "C");
map1.put(5, "E");
 
//map 2
HashMap<Integer, String> map2 = new HashMap<>();
 
map2.put(1, "G");   //It will replace the value 'A'
map2.put(2, "B");
map2.put(3, "C");
map2.put(4, "D");   //A new pair to be added
 
//Merge maps
map1.putAll(map2);
 
System.out.println(map1);