Multiple interface inheritance problem.

[Varun Narang]

Hi all,

I was trying and not able to understand the behaviour of code that'd satisfy the multiple inheritance for following case;

class MyException extends Exception	{
	
}

class MyException2 extends Exception	{
	
}

interface Hello1	{
	public String sayHello() throws MyException;
	public void greet();
}

interface Hello2	{
	public String sayHello() throws MyException2;
	public Object greet();
}


public class InheritanceTest implements Hello1, Hello2 {
        // what goes here for method signature, return type and Exception thrown for:
        // 1) for method name sayHello w.r.t to Exception being thrown.
        // 2) for method greet
	
}

If any once can please explain the behaviour and implementation in respective cases, it'd be a great help.

Thanks & Regards,
+ Varun

[David Newton]

As far as I know you wouldn't be able to do this.

First, consider greet(). Even ignoring inheritance, you're not allowed to have two methods that differ only by their return type.

Check out this section in the JLS.

[Rob Spoor]

Ignoring the greet() method problems, there is only one way to be able to satisfy the contract for both Hello1.sayHello() and Hello2.sayHello() - by throwing no exceptions at all. After all, if it throws MyException it violates the contract for Hello2.sayHello(), and if it throws MyException2 it violates the contract for Hello1.sayHello().

[Varun Narang]

@David, Thanks for the advice, I'll keep that in mind.

@Rob, I was thinking in the similar direction, Thanks for confirming. This is more of a 'obey the contract' problem than a programming puzzle.

Thanks once again.

Regards,
Varun.

[Jim Hoglund]

Yes, an attempt to implement the interfaces show both incompatible
return type and incompatible exception type errors.

Jim ... ...