I am preparing for the SJCP exam, and want to verify a fact I found
in a book regarding Interfaces & Abstract classes.

I tried verifying it, by writing code and found otherwise so want to
confirm.

It mentions.. Abstract classes & interfaces are very similar in their
structure & implementation, however one differece is abstract class
does not have to have any methods, whereas an interface must have
atleast one empty method. --> I tried verifying this and found that
you can define and extend/implement either the abstract class or the
interface without any methods defined in them.