Why does the Java compiler sometimes allow the unboxing of null?

Question

For example:

int anInt = null;

fails at compile time but

public static void main(String[] args) {
  for (int i = 0; i < 10;          


        

Answer 1

Boxing partially hides the distinction between primitives and corresponding wrapper objects, but it doesn't remove it.

There are two distinctions which are not changed by boxing:

• objects can be null, while primitives cannot
• objects have both state and identity, while primitives have only state (the value)

Occasionally, these differences can cause problems when using boxing.

Some points to remember :

• be careful with nulls. Auto-unboxing a null object will cause a NullPointerException.
• comparing items with == and equals must be done with care.