What is the interface and how will you go about implementing interface?

Answer 1

As defined in the java programming language 4th edition:

The fundamental unit of programming in the Java programming language is the class, but the fundamental unit of object-oriented design is the type. While classes define types, it is very useful and powerful to be able to define a type without defining a class. Interfaces define types in an abstract form as a collection of methods or other types that form the contract for that type. Interfaces contain no implementation and you cannot create instances of an interface. Rather, classes can expand their own types by implementing one or more interfaces. An interface is an expression of pure design, whereas a class is a mix of design and implementation.

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The idea behind this that an interface is just a "contract" where you can define methods a class will implement (better said (in OOP:) messages), but within the interface there are only signatures. No behavior for those methods... Then it class that implemets the interface will understand and provide an implementation for those methods (messages). So you can have a lot of diferents classes that implement the same interface and in any place you need that interface you can use any of those classes... that's one of the benefit of interfaces...

e.g.:

interface LifeBeing{

void breath();

}

public class Human implements LifeBeing {

void breath(){

// do something;

}

}

public class Three implements LifeBeing {

void breath(){

// do something else;

}

}