User-defined Interfaces

In Java, User-defined Interfaces are interfaces that you create to define a contract that classes must follow. These interfaces allow you to define abstract methods without providing implementations. Classes that implement the interface must provide their own implementations for the abstract methods.

Key Points:

  • A user-defined interface can contain abstract methods (methods without implementations) and constants (static final variables).
  • A class that implements a user-defined interface must provide an implementation for all abstract methods in the interface.
  • Multiple interfaces can be implemented by a single class.

Example of User-defined Interface:

Defining an Interface:

interface Animal {
    void sound();  // Abstract method
    void move();   // Abstract method
}

Implementing the Interface in a Class:

class Dog implements Animal {
    @Override
    public void sound() {
        System.out.println("Bark");
    }

    @Override
    public void move() {
        System.out.println("Dog runs");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.sound();  // Output: Bark
        dog.move();   // Output: Dog runs
    }
}

Example of Multiple Interfaces Implementation:

interface Animal {
    void sound();
}

interface Mammal {
    void move();
}

class Dog implements Animal, Mammal {
    @Override
    public void sound() {
        System.out.println("Bark");
    }

    @Override
    public void move() {
        System.out.println("Dog runs");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.sound();  // Output: Bark
        dog.move();   // Output: Dog runs
    }
}

🔗 Related Notes