Introduction

• Default methods are methods in an interface that have a method body.
• They were introduced in Java 8 to allow interfaces to have concrete methods without affecting classes that already implement the interface.
• Declared using the default keyword.
• They provide a way to add new methods to interfaces without breaking existing code that implements them.
• Default methods are also known as defender methods or virtual extension methods.

• Uses of Default Methods:
  • To add new functionality to an interface without forcing all implementing classes to override it.
  • To provide a default implementation that can be inherited by implementing classes.
  • To enable backward compatibility — old classes implementing the interface will still work even after new methods are added.
  • To support multiple inheritance of behavior (since a class can implement multiple interfaces with default methods).

Program:

• Below is the program for Default methods in an Interface:

  interface MyInterface
  {
      // Abstract method (must be implemented by implementing classes)
      void m1();
  
      // Default method (has a body, optional to override)
      default void m2()
      {
          System.out.println("This is a default method inside an interface.");
      }
  }
  
  class MyClass implements MyInterface
  {
      @Override
      public void m1()
      {
          System.out.println("Implementation of abstract method.");
      }
  }
  
  public class MainApp1
  {
      public static void main(String[] args)
      {
          MyClass obj = new MyClass();
          obj.m1();   // Calls implemented abstract method
          obj.m2();   // Calls interface default
      }
  }

  Output:

  Implementation of abstract method.
  This is a default method inside an interface.