Interfaces

An interface in Java is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. Interfaces define a contract that classes must implement.

Key Points:

  • A class can implement multiple interfaces.
  • Interfaces provide a way to achieve abstraction by allowing methods to be declared without providing their implementation.
  • An interface can be used to define common behaviors that multiple classes can share.

Example of Defining and Implementing an Interface:

Defining an interface:

interface Animal {
    void sound();
}

Implementing the interface in a class:

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

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

Example with Multiple Interfaces:

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