What is Interface in Java ?
An interface in java is a blueprint of a class. It has static constants and abstract methods only.The interface in java is a mechanism to achieve fully abstraction. There can be only abstract methods in the java interface not method body. It is used to achieve fully abstraction and multiple inheritance in Java. An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface. An interface is not a class. Writing an interface is similar to writing a class, but they are two different concepts. A class describes the attributes and behaviours of an object. An interface contains behaviours(Abstract Methods) that a class implements. Unless the class that implements the interface is abstract, all the methods of the interface need to be defined in the class.Since multiple inheritance is not allowed in java so interface is only way to implement multiple inheritance.