I understand object variables get intialized to NULL if you do not initialize them explicitly and accessing them will give null pointer exception where as this does not happen for primtive variables as get their values to defaults automatically. Is that a good understanding?
The null value can be considered the default value for reference variables. In addition: Only the member variables get automatically initialized to default values; local variables are not. However, the components of an array are initialized to default values even when the array was local to a method.