Interface

• Interfaces can be _public _ or default access.
• Cannot be instantiated.
• Interfaces are Always abstract.
• Can be empty
• Cannot be final
• A class may implement multiple interfaces.
• An interface can extend Another interface.
• Methods in an interface are Always public abstract
• First Concrete class that implements an interface has to implement all of its inherited abstract methods.
• An abstract class inherits methods of the interface it is extending, but it does not have to implement them.

Interface variables

• Always public, static and final.
• Value has to be set when declared in the interface.

Default interface method (java 8)

• a method defined in the interface body.
• Use default keyword.
• The class may override the default method.
• Allows backwards compatibility since default methods are not needed to be implemented in the class implementing the interface. Allows libraries to be updated without affecting the code.
• Only in interface and is public.
• If same default method is defined in two interfaces implemented in a class, then compilation would fail.

Static interface method (java 8)

• Is implemented in the interface
• Is not inherited in any class implementing the interface
• Is public
• The name of the interface has to be used to access the method.