AbstractMethodError

[Sudarshan Sreenivasan]

Hi

Can you tell me when a AbstractMethodError occurs ?? The api says

Thrown when an application tries to call an abstract method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last compiled.

I need an example situation of when this can happen at runtime ?? , I can not think of a situation where this could happen, can anyone throw light on it

Thanks
Sudarshan

[Ernest Friedman-Hill]

Create an empty interface

interface I {}

Create a class that implements it:

class C implements I {}

Now compile them both.

Now modify the interface:

interface I { void m(); }

Compile interface I, if you like, but do not compile class C.

Now create a class which uses the interface.

public class A {
    public static void main(String[] argv) throws Exception { 
        I i = (I) Class.forName("C").newInstance();
        i.m();
    }
}

Compile only class A and run it, and you'll get an AbstractMethodError. Class C has not been compiled since interface I changed, so it does not include an implementation of method m().