Question: What are interfaces?

Answer: Interfaces provide more sophisticated ways to organize and control the objects in your system.
The interface keyword takes the abstract concept one step further. You could think of it as a 'pure' abstract class. It allows the creator to establish the form for a class: method names, argument lists, and return types, but no method bodies. An interface can also contain fields, but The interface keyword takes the abstract concept one step further. You could think of it as a 'pure'?? abstract class. It allows the creator to establish the form for a class: method names, argument lists, and return types, but no method bodies. An interface can also contain fields, but an interface says: 'This is what all classes that implement this particular interface will look like.'?? Thus, any code that uses a particular interface knows what methods might be called for that interface, and that'??s all. So the interface is used to establish a 'protocol'?? between classes. (Some object-oriented programming languages have a keyword called protocol to do the same thing.)  Typical example from "Thinking in Java":

import java.util.*; 
interface Instrument { 
	int i = 5; // static & final 
	// Cannot have method definitions: 
	void play(); // Automatically public 
	String what(); 
	void adjust(); 
}
 
class Wind implements Instrument { 
	public void play() { 
		System.out.println("Wind.play()"); 
	}
	public String what() { return "Wind"; } 
	public void adjust() {} 
}