In a non-static method is the method duplicated every time an object is created?

Question

for example, lets say you have:

class X
{
    public void foo()
    {

    }

}

and then in your main you have

X anX = new X();
anX.foo();
X bX = new X();
bX.foo();

is the "foo" method being duplicated for every instance of X? Or is it that each instance just re-uses the foo method code.

Answer 1

It will reuse the method code for each object. What changes is the implicit argument, which is the object you invoke the method on.

Answer 2

Instance methods are despatched (more or less) using a Class pointer and an internal virtual-method table. Similar, but slightly more indirect & slower, for methods accessed via an interface.

Class VMTs and method code are loaded once per ClassLoader & then shared between all objects using the method. Thus class type information & method code are not duplicated in memory.

Objects always keeps their Class pointer and the (internal) virtual-method table. This applies whether casting to a subtype or assigning to a supertype. Object Class and the internal pointer are assigned at construction and invariant for the lifetime of the object.

Static methods OTOH are not virtualized, do not use a VMT & despatch according to the static type of the reference. This is resolved at compile time.