The java.awt.FontMetrics class is declared abstract but defines no methods to
actually be abstract. The implementation of stringWidth() calls charsWidth().
The implementation of charsWidth() calls stringWidth(). If the class is
extended but charsWidth() not redefined, a call will result in infinite
recursion.

[jim.graham@Eng 1997-02-20]
I put a big note to subclassers in the class comments warning them to implement
enough methods to avoid the recursion. I even suggested which methods should
be implemented.

That's the best we can do with this - we can't remove one of the methods in
case some subclass out there is relying on it. I will close this bug as
"will not fix".