Java reflection: Access methods of classes that extend a class

Am developing an interpreter in Java and for easy extensibility, I am using some reflection at startup time so functions can be called just by their name.

So far I had the following structure of classes:

A extends B
B extends C
C extends D

And to access ALL the methods defined in any of those classes I used:

Method method = A.class.getMethod("theExpectedFunctionName");

That works.

However now that the project grew it turned out that it would be much more comfortable to have a class structure like:

B extends A
C extends A
D extends A

But now the getMethod function naturally doesn't work like that anymore. Is there a way how I can retrieve all methods that are in children classes of A?

Huge thanks in advance!