Difference between Interface and Abstract Class?

An interface declares a set of related methods, outside of any class

An abstract class is an incomplete class definition that declares but does not define all of its methods

An interface defines an API that is independent of any class hierarchy. Interfaces are the ultimate encapsulators, but they hide all the details of the classes that implement their methods from the user of the interface.

Unlike an interface, an abstract class is a proper class. Unlike a concrete class, some of its behaviors are deliberately left to be defined by its own subclasses. Abstract classes cannot be instantiated because of this - only instances of concrete subclasses can be created.