Java runnable and interfaces

Question

I'm trying to implement a UserInterface interface, which always needs to run in a thread (so is Runnable). So I have code like this, where SpecificInterface implements UserInterface:

UserInterface myUI = new SpecificInterface(...);
Thread thread = new Thread(myUI);
thread.start();

But this obviously doesn't work, because I can't make UserInterface implement Runnable since interfaces can't implement other interfaces. And I can't just make SpecificInterface runnable since that defeats the point of using interfaces.

How am I supposed to make this work? Do I need to make UserInterface an abstract class, or create a RunnableInterface abstract class which implements UserInterface and Runnable and inherit my UI's from it, or..? I am rather confused as to why the "simple" solution can't work.

Googling was less than helpful, all I find is links telling me how to use the "Runnable interface" :|

@JoshM They are way too big to be shown here. But basically they all have a custom event dispatcher loop in the run() method (this is for an exercise). — Thomas
– Thomas, Commented Aug 28, 2013 at 3:57

Ted Hopp · Accepted Answer · 2013-08-28 03:51:50Z

3

Interfaces can extend other interfaces.

interface UserInterface extends Runnable {
    void someOtherFunction();
    // void run() is inherited as part of the interface specification
}

public class SpecificInterface implements UserInterface {
    @Override
    public void someOtherFunction() {
        . . .
    }

    @Override
    public void run() {
        . . .
    }
}

answered Aug 28, 2013 at 3:51

Ted Hopp

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3 Comments

Josh M Over a year ago

UserInterface would have to extends Runnable. It appears that SpecificInterface is a sub-interface of UserInterface (judging from his declaration statement).

Ted Hopp Over a year ago

@JoshM - Sorry; I had names backwards.

Thomas Over a year ago

That works great, thanks! Didn't know about extending interfaces!

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