Question

I know that fields stick to the objects as long as they exist, so they have some memory allocated, but what if I don’t initialize some fields and don’t use them? For example:

public class TEST {
   public static void main(String[] args) {
      Foo C = new Foo(5, 7);
      Foo D = new Foo(5);
      ...
}

public class Foo{
   private int A;
   private float B;

   public Foo (int A, float B){
      this.A = A;
      this.B = B;
    }
    public Foo (int A){
        this.A = A;
    }
    ...
}

Will C consume more memory than D?

Answer 1

Fields in Java are always initialized. Primitives are initialized to 0 or false, and references (and arrays) are initialized to null.

Furthermore, once you declare a field, that field will always take up the same space in every instance. References take up only as much space as a pointer, but the referred-to object might take extra memory.