Question

I have an interface containing void doThis();. I’ve implemented the interface in my Main class and it automatically added public void doThis() { ... } to my class. If I’m in Second class, how do I invoke doThis() in Main?

Answer 1

When you implement an interface, you’re making a class. Interfaces are implemented by instance methods on that class.

To invoke an instance method on a class, instantiate the class, and invoke it as you would any other instance method:

Main m = new Main();
m.doThis();

Per my example code, you might want to pass an instance of Main into Second instead of creating the instance inside Second. You can pass this in via the interface instead of via the concrete class type:

public class Second
{
    public void doSomething(SomeInterface si)
    {
        si.doThis();
        // other code here...
    }
}

// Some code outside those classes, that uses both classes...

Second s = new Second();
SomeInterface si = new Main();
s.doSomething(si);