What is interface?

An interface from a software application perspective is a window which a user deals with. For instance, when you run the calculator application in your window operating system, the window that pops up is the interface for the calculator application. You hit keys on your keyboard entring numbers and then you click on the button with equal sign to get the result. You may have no idea what's going on behind the scene. All you care about is what you can see on the interface. In other words an interface is the border between the machine and the user. You communicate with the machine through an interface. 

In the real world, an interface could be the plastic sheet that cover a DVD player with a bunch of buttons that play, stop, pause, and eject the disc from the player.

an interface is a group of related methods with empty bodies

Interface is similar to class.but they lack instance variable ,and the methods are declared without body inside interface.

interface is collection of abstactmethods and final variables,

it is used insted of multiple inheritance

we cant create object for interface

• InterfaceA contract initially planned to cover various aspects of one single job. Each indivisual aspect is taken as a procedure of which signature you define inside and use it in your class to add functionality inside. They are not to just define method signatures inside and use them later in other classes but to ensure the compactness of given module. If a single step is not performed or missed intentionally or unintensionally, compiler helps remembrize you the step(method) you not performed (overridden).