Explain the concept of Interface.

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Java Interface

An interface is a fully abstract class. It includes a group of abstract methods (methods without a body).

We use the interface keyword to create an interface in Java. For example,

interface Language {
  public void getType();

  public void getVersion();
}

Here,

  • Language is an interface.
  • It includes abstract methods: getType() and getVersion().

Implementing an Interface

Like abstract classes, we cannot create objects of interfaces.

To use an interface, other classes must implement it. We use the implements keyword to implement an interface.

Example 1: Java Interface

interface Polygon {
  void getArea(int length, int breadth);
}

// implement the Polygon interface
class Rectangle implements Polygon {

  // implementation of abstract method
  public void getArea(int length, int breadth) {
    System.out.println("The area of the rectangle is " + (length * breadth));
  }
}

class Main {
  public static void main(String[] args) {
    Rectangle r1 = new Rectangle();
    r1.getArea(5, 6);
  }
}

Output

The area of the rectangle is 30

In the above example, we have created an interface named Polygon. The interface contains an abstract method getArea().

Here, the Rectangle class implements Polygon. And, provides the implementation of the getArea() method.