Answer Posted / arvind

1.interface contains methods that must be abstract;
abstract class may contain concrete methods.
2.interface contains variables that must be static and
final; abstract class may contain non-final and final
variables.
3.members in an interface are public by default, abstract
class may contain non-public members.
4.interface is used to "implements"; whereas abstract class
is used to "extends".
5.interface can be used to achieve multiple inheritance;
abstract class can be used as a single inheritance.
6.interface can "extends" another interface, abstract class
can "extends" another class and "implements" multiple
interfaces.
7.interface is absolutely abstract; abstract class can be
invoked if a main() exists.
8.interface is more flexible than abstract class because
one class can only "extends" one super class,
but "implements" multiple interfaces.
9.If given a choice, use interface instead of abstract
class.

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