Interface
Interface provides a standards that to be implemented in a
related class.
Implementing an interface allows a class to become more
formal about the behavior it promises to provide. Interfaces form a contract
between the class and the outside world, and this contract is enforced at build
time by the compiler. If your class claims to implement an interface, all
methods defined by that interface must appear in its source code before the
class will successfully compile.
Rules:
By
default all methods in interface are public and abstract. (No need to mention
it explicitly)
Variables
declared in interface are by default public, static and final.
Implemented
class guaranty that all methods declared in the interfaces are defined unless
the class is not abstract.
Class
can implement any number of interfaces
Interface
can extend any number of interfaces
Example
interface User { float PI=3.14f; // becomes constant, by default it uses public static final keyword void add(); // declaration, by default it uses abstract and public void update(); void delete(); }
class Manager implements User { public void add() // public keyword should be explicitly given in class { System.out.println(?adding manager?); } public void update() { System.out.println(?updating manager?); } public void delete() { System.out.println(?deleting manager?); } }