Differences between interface and abstract class

The interfaces and abstract classes, both can't be instantiated. While an abstract class contains both implemented and non-implemented methods, an interface contains only abstract methods.

INTERFACE

• An interface is pure contract
• Interface must be public
• It may be left unused after declaration
• When used, Implementing class must override all methods provided by that interface.
• It contains only unimplemented methods and no function definitions
• Variable must be abstract and final
• Methods take abstract as default.
• A single class can implement multiple interfaces.
• Interface properties are included with "implements" key word

ABSTRACT CLASS

• Abstract class must contain at least one abstract method
• It can contain function body
• It contains both implented and unimplemented method.
• It allows both abstract and non abstract methods.
•  It must be used if declared, otherwise compiler gives an error.
• It may be public or protected.
• Only one class can extend abstract class.
• Abstract properties are included with extends keyword.