interface question

[mark stone]

interface One
{
public void someMethod();
}
public class One_impl implements One
{
public native void someMethod();
}

Assuming that the native method is not provided in any local library, an attempt to compile and run the above lines of code will cause

1 Compilation error - implimentations can never be native.
2 Compilation error - method not found in local libraries.
3 Runtime Exception - method not found in local libraries.
4 Compilation successfull but runtime error is thrown if and only if the method someMethod of class One_impl is called.

[Rob Ross]

This isn't really an interface question, it's an implementation question.
The interface simply defines a particular method signature.
In the class, you are implementing that method. You are using a native method for the actual implementation. When you compile, the native keyword tells the compiler "Hey, don't worry about compiling this method, it's not written in java. I promise you'll find it *someplace* when I run it. Honest."
But since you haven't actually written an implementation for it, or loaded a library, if you try to call it, the VM won't be able to find the implementation, so it won't be able to run that method, so you'll get a runtime error.

If you never try calling the method, then you'll never have a problem, because the VM won't have to look for the method implementation.

Rob
[ January 30, 2002: Message edited by: Rob Ross ]

[mark stone]

so the answer is 3 or 4 ?
because now we know that there cannot be any compilation problem as the compiler has not specifically told about it.

Originally posted by Rob Ross:
This isn't really an interface question, it's an implementation question.
The interface simply defines a particular method signature.
In the class, you are implementing that method. You are using a native method for the actual implementation. When you compile, the native keyword tells the compiler "Hey, don't worry about compiling this method, it's not written in java. I promise you'll find it *someplace* when I run it. Honest."
But since you haven't actually written an implementaion for it, and loaded a library, if you try to run it, the VM won't be able to find the implementation, so it won't be able to run that method, so you'll get a runtime error.

If you never try calling the method, then you'll never have a problem, because the VM won't have to look for the method implementation.

Rob

[Rob Ross]

Answer is 4
Rob.