What is a NullPointerException or java.lang.NullPointerException ?

A NullPointerException means that one of the variables you are passing is null, but the code tries to use it like it is not.

For example, If I do this:

Integer myInteger = null;int n = myInteger.intValue();

The code tries to grab the intValue of myInteger, but since it is null, it does not have one: a null pointer exception happens.