What’s the precise Use of interface in Java?

An interface in Java has remained a posh subject for a lot of freshmen to grasp. The very first thing which puzzles many programmers is the truth that you can not outline any technique inside interface, it a simply declaration. By rule, all technique inside interface have to be summary (Nicely, this rule is altering in Java 8 to permit lambda expressions, now interface can have one non-abstract technique, also called a default technique). So, if you cannot outline something, Why we’d like an interface?  what’s the usage of an interface, if we’re anyway going to jot down a category and override them to supply behaviour, Cannot we declare these strategies inside the category itself with out utilizing interface and so on. Nicely, if you’re considering by way of behaviour then you might be actually lacking the purpose of interface.

I believe one has to learn Efficient Java, to grasp greatest use of interface. Interface is nice to declare Kind, they promote code reusability, and they’re the true driver of polymorphism in Java.

The interface additionally permits a number of inheritance in Java, which makes it doable for a category to grow to be Canvas, in addition to EventListener, which is used to attract graphics in addition to to to course of occasions. 


On this submit, I’ll share few factors, which is able to aid you to grasp what’s the precise use of interface in Java. By the way in which, if you’re confused between summary class and interface, then you might wish to learn my earlier submit on distinction between interface and summary class in Java. 

Why we’d like Interface in Java?

There are a number of causes, an software developer wants an interface, certainly one of them is Java’s characteristic to supply a number of inheritance at interface stage. It means that you can write versatile code, which might adapt to deal with future necessities. A number of the concrete causes, why you want interface is :

1) In the event you solely implement strategies in subclasses, the callers will be unable to name them by way of the interface (not widespread level the place they’re outlined).

2) Java 8 will introduce default implementation of strategies contained in the interface, however that must be used as exception slightly than rule. Even Java designer utilized in that means, it was launched to take care of backward compatibility together with supporting lambda expression. All evolution of Stream API was doable on account of this transformation.

3) Interfaces are a solution to declare a contract for implementing lessons to fulfil; it is the first device to create abstraction and decoupled designs between customers and producers.

Right here is an instance of how interface helps a number of inheritance in Java

interface Canvas{
  public void paint(Graphics g);
}

interface EventListener{
  public boolean course of(Occasion e);
}

pubic class Recreation implements Canvas, EventListener{

 @Override
 public void paint(Graphics g){
   g.drawLine(Shade.RED);
 }

 @Override
 public boolean course of(Occasion e){
   KeyCode code =  e.getKeyPressed().getCode();
 }

}

5) Interface is vital to API design. In truth, a smaller interface like Comparable, Runnable, Callable makes the core of Java API. Although nice care is required whereas designing and publishing an interface, as a result of as soon as revealed, you cannot change the interface with out breaking apart all of your shoppers, i.e. lessons which have carried out your interface. 

6)  “Programming to interface than implementation” is among the fashionable Object-oriented design rules, and the usage of interface promotes this. A code written on the interface is far more versatile than the one which is written on implementation.

7) The usage of interface means that you can provide a brand new implementation, which could possibly be extra strong, extra efficiency within the later levels of your improvement.

Briefly foremost use of the interface is to facilitate polymorphism. the interface permits a category to behave like a number of varieties, which isn’t doable with out a number of inheritances of sophistication. It additionally ensures that you simply observe programming to the interface than the implementation sample, which ultimately provides quite a lot of flexibility in your system.