Default methods (default)

Introduced in Java 8, default methods allow interfaces to provide concrete method implementations without breaking existing code. They are defined with the default keyword.

Purpose:

• Evolve interfaces by adding new methods without forcing all implementing classes to provide implementation.
• Provide common behavior that can be overridden if needed.

Syntax:

interface Vehicle {
    void start();

    default void honk() {
        System.out.println("Beep beep!");
    }
}

Using default methods:

class Car implements Vehicle {
    @Override
    public void start() {
        System.out.println("Car starting");
    }
    // honk() is inherited (can be overridden optionally)
}

Car car = new Car();
car.start();  // Car starting
car.honk();   // Beep beep!

Overriding default methods:

class ElectricCar implements Vehicle {
    @Override
    public void start() {
        System.out.println("Electric car silently starts");
    }
    @Override
    public void honk() {
        System.out.println("Electric beep");
    }
}

Conflict resolution: When a class implements multiple interfaces with conflicting default methods, the class must override the method. Use InterfaceName.super.methodName() to call a specific default.

Note: Default methods are not allowed to override Object class methods (e.g., equals, hashCode).