Dereferencing happens with the
Object obj = new Object(); String text = obj.toString(); // 'obj' is dereferenced.
Dereferencing follows the memory address stored in a reference, to the place in memory where the actual object resides. When an object has been found, the requested method is called (
toString in this case).
When a reference has the value
null, dereferencing results in a NullPointerException:
Object obj = null; obj.toString(); // Throws a NullpointerException when this statement is executed.
null indicates the absence of a value, i.e. following the memory address leads nowhere. So there is no object on which the requested method can be called.