Different Ways of Creating HashMaps

Question

I've been learning about HashMaps recently but I have one question that I can't seem to get a clear answer on. The main difference between -

HashMap hash1 = new HashMap();

vs

HashMap<,>hash1 = new HashMap <,> (); //Filled in with whatever Key and Value you want. 

I thought when you define a HashMap it requires the Key and Value. Any help would be much appreciated. Thank You.

Answer 1

Those are the options you have:

J2SE <5.0 style:

 Map map = new HashMap();

J2SE 5.0+ style (use of generics):

 Map<KeyType, ValueType> map = new HashMap<KeyType, ValueType>();

Google Guava style (shorter and more flexible):

 Map<KeyType, ValueType> map = Maps.newHashMap();

Answer 2

You should take a look on Java generics, if you don't specify the types of the HashMap, both key and value will be Object type.

So, if you want a HashMap with Integer keys and String values for instance:

    HashMap<Integer, String> hashMap= new HashMap<Integer, String>();