When java doesn't support pointers. why does it throws null pointer exception?

When you see "NullPointException", it means that you are using a variable that is not instantiated.

Any Java variable you declare, then instantiate by the 'new' keyword, will "point" to a location in memory.  It is a reference to this location. NullPointerException is just a name, it could be anything.  When you try to use a variable which is NOT YET instantiated, it points nowhere and can do noting. hence the exception.