[Interface] No fields can be defined in interfaces [Abstract class] An abstract class can have fields and constrants defined [Feature] 
Fields and Constants
M u l t i p l e i n h e r i t a n c e
D e f a u l t i m p l e m e n t a t i o n
A c c e s s M o d f i e r s
C o r e V S P e r i p h e r a l
H o m o g e n e i t y
S p e e d
A d d i n g f u n c t i o n a l i t y ( V e r s i o n i n g )
F i e l d s a n d C o n s t a n t s