A class that is declared as abstract is known as abstract class. It needs to be extended and its method implemented. It cannot be instantiated.
No, if there is any abstract method in a class, that class must be abstract.
No, because abstract method needs to be overridden whereas you can't override final method.
Interface is a blueprint of a class that have static constants and abstract methods.It can be used to achieve fully abstraction and multiple inheritance.
No, because methods of an interface is abstract by default, and static and abstract keywords can't be used together.
No, because its implementation is provided by another class.
An interface that have no data member and method is known as a marker interface.For example Serializable, Cloneable etc.
No, they are implicitly public.
Basically Java doesn't allow multiple inheritance, so a Class is restricted to extend only one Class. But an Interface is a pure abstraction model and doesn't have inheritance hierarchy like classes(do remember that the base class of all classes is Object). So an Interface is allowed to extend more than one Interface.
