Answers for "What’s null pointer exception?"

null pointer exception

NullPointerExceptions are exceptions that occur when you try to 
use a reference that points to no location in memory (null)
 as though it were referencing an object.

What’s null pointer exception?

First, null keyword it does not refers to any object at all. 
Null keyword means no object.
null pointer excep: there is no object at all.
So you can't get access to the instance of that object