1. Addition

Map<Integer, String> map = new HashMap<>();
map.put(1, "First element."); 
System.out.println(map.get(1));

Output: First element.

1. Override

Map<Integer, String> map = new HashMap<>();
map.put(1, "First element.");
map.put(1, "New element.");
System.out.println(map.get(1));

Output: New element.

HashMap is used as an example. Other implementations that implement the Map interface may be used as well.