Question

If I have a class A which is super class of classes B and C and I have

A as[] = new A[1];

then how much space will as occupy the size of A, B or C?

Answer 1

The object as is an array of length 1. In Java, arrays containing objects actually contain references to objects, and a reference takes either 4 or 8 bytes depending on the hardware architecture.

You haven’t allocated any objects of type A, or any of its subtypes, so the total memory used is the memory occupied by a single reference (4 or 8 bytes).

If you were to do

as[0] = new A();

then you would additionally have however much memory A takes up, which depends on what A contains. If you did

as[0] = new B();

the memory usage would be whatever B takes up, which depends on B‘s members but would be ≥ A‘s memory requirements.