As Knute says, the abstract method can be declared again in an abstract subclass, but it definitely doesn't have to be. A normal (non-abstract) class just has to implement all the abstract methods it has inherited from parent class(es) and interfaces.
I can imagine only a few reasons to declare an method class again in an abstract class:
The new declaration returns more specific type than the original class (for example, the parent class method might return a Number, while the child class method returns a Double.
The new declaration has a broader scope than the original one, for example public instead of protected (it looks like a questionable design, though).
The new declaration is accompanied by a more specific comment than the one provided by the parent class.
Personally, I'd avoid declaring the abstract method in the child class again without a good reason.
I agree with Martin that it usually isn't a good idea to redeclare such a method. If you do redeclare it, be sure to use the @Overrideannotation, to detect any tiny spellling errors you might have made.