can a class be extended by interface in java? why?

Question

I appared for an interview with on of the IT companies. They asked me "can a class be extended by interface in java? why?". Of course we know that it can not be extended. But I had no justification for why.

Answer 1

No, Interface only has declaration. Interface does not have definations. So class can have declaration and definations. If you try to extend class by interface, you will break basic rule. So ultimatly compiler will throw an error.

 

Valid:

import java.rmi.Remote;

 

public interface MyInterface extends Remote{

 

}

 

and

 

import org.openqa.selenium.remote.RemoteWebDriver;

 

public class myClass extends RemoteWebDriver{

 

}

 

invalid:

 

import org.openqa.selenium.remote.RemoteWebDriver;

 

public interface myInterface extends RemoteWebDriver{

 

}

Hope above example helps.