Solved! Quick Java question.

[Amol S.]

Note that whenever I say classA, I am referring to a abstract class that is the parent of a regular class that is called classB.
Is the bellow code:

classB b = new classB();
classA refer = b;

the same as:

classA refer = new classB();

or are they both different?

 

[Cogman]

They are functionally equivalent.

The type in java enforces that the assigned value is the same type or subtype. It does not do any sort of conversion. What's actually stored is the reference value.

This is why this is safe

Integer a = 1;
Number b = a;
Integer c = (Integer)b;

The only allocation that happened is the initial boxing assignment of a. After that, java is just setting b and c to the a reference.

This is also why this is invalid

Integer a = 1;
Number b = a;
Double c = (Double)b;

That's because Double is not a subtype of integer so the JVM is not capable of doing that assignment.

The rules around primitive types are different ( int i = (double)4.2; is valid). However, for all objects, they are consistent.