Question

Can you have a class which implements an interface, and choose whether to use the methods in the interface during instantiation of this class? Therefore having object A which uses the interface and object B which does not use it.

Thanks

Updated:

Assuming you have a Professor class and this class implements an interface called Employer, which has employ(rAssist x) abstract method.

Now I want to instantiated 2 objects from the Professor class implementing this interface Object A – Professor can employ a research assistant and Object B – Professor cannot employ research assistants.

Answer 1

Can you have a class which implements an interface, and choose whether to use the methods in the interface during instantiation of this class?

No, if class C implements the interface, then all instances of C will provide the methods declared in the interface.

What you can do is something like

class MyClass implements MyInterface {

    @Override
    void interfaceMethod() {
        System.out.println("Interface method");
    }
}

and then do

MyClass x = new MyClass();

MyClass y = new MyClass() {
    @Override
    void interfaceMethod() {
        throw new UnsupportedOperationException();
    }
};

In effect, x supports the use of interfaceMethod while y does not. Note however that…

• The usage of y.interfaceMethod is not prevented at compile-time, i.e. it will not be enforced by the type system.

• With this solution, you are in fact creating an (anonymous) subclass of MyClass and assigning an instance of it to y.