Which two method you need to implement for key Object in HashMap ?

Question

Example
Map data = new HashMap();
data.put("a","America");
data.put("a","Africa");
data.put("b","Bangladesh");

Need to have both "America" and "Africa" as value against key "a". Is there any mechanism to achieve this scenario.

Answer 1

In order to use any object as Key in HashMap, it must implements equals and hashcode method in Java. Read How HashMap works in Java for detailed explanation on how equals and hashcode method is used to put and get object from HashMap.