Answer Posted / brijendra-java (xavient)

HashMap is the implementaion of Map interface.
HashMap is key value pair storage concept.
HasMap does not allow duplicate key but value may be any
thing.
HasMap allow both key and Valuea as NULL.
HasMap is the Unordered collection.
When we change the iteration of HasMap then it give
concurrent Modification error.
HasMap is NonSyncronised class.

HashMap hMap = new HashMap();
hMap.put(Null, Null);
hMap.put(1, a);
hMap.put(2, b);
hMap.put(3, c);
system.out.println("Size"+hMap.size());

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