NullPointerException

Question

What is an NullPointerException? What does it mean? And what can I do to avoid it?
Thanks for your help!

Answer 1

This is when you try to do an illegal operation with a null pointer, like trying to dereference it.

Answer 2

In java ? Usually you havent initialize the object but trying to use it.

Ex.
PrintWriter file;
file.println("lol");
//This will cause nullpointer error

Answer 3

Both are right! Thank you so much!!! You helped me a lot!!