Question

I have a method on the current object that takes a parameter. Invoking the method throws a NullPointerException, even though this by definition must not be null.

private String doSomething(int i){
   return "I";
}

Invocation:

Integer i = null;
String s = this.doSomething(i);

Why is there a NullPointerException if I’m not referencing a null object?

Answer 1

In this case the JVM internals are throwing a NullPointerException because of the inability to convert a Integer i to the int i. In this case the Integer is null, which of course is not valid for the primitive data type int.

This is not a permitted conversion, per the specification, and noted in the guide for Java 1.5.