What is the difference between referencing a field by class and calling a field by object?

Question

I have noticed that there are times when coding in Java that I have seen fields called by method:

System.out.println(object.field);

and

Answer 1

Instance scope versus class scope.

Check this out:

class Foobar {
  public final int x = 5;
  public static final int y = 6;
}

y is a variable that is only created once, at compile time. It is bound to the class, and therefore shared by all of its instances. You reference this with Foobar.y.

System.err.println(Foobar.y);

x on the other hand, is an instance variable, and every Foobar that you create with new will have a copy of it. You would reference it like this:

Foobar foobar = new Foobar();
System.err.println(foobar.x);

But this will not work:

System.err.println(Foobar.x);