Java.Java8.How do I call the default method of an interface in a class that implements this interface?

Calling a default method from an interface inside a class that implements it is straightforward, and it becomes especially important when there’s a conflict between multiple default methods.

✅ How to Call a Default Method in a Class

If you’re in a class that implements the interface, and you want to explicitly call the default implementation, use this syntax:

InterfaceName.super.methodName();

🧠 Example:

interface Greetable {
    default void greet() {
        System.out.println("Hello from Greetable");
    }
}

class Person implements Greetable {
    @Override
    public void greet() {
        System.out.print("Person says: ");
        Greetable.super.greet(); // Calls the default method
    }
}

new Person().greet(); // Output: Person says: Hello from Greetable

⚔️ Why Use InterfaceName.super.method()?

• To reuse default implementation
• To resolve conflicts when your class implements multiple interfaces with the same method

⚠️ Important Notes

1. You can only call it from within an instance method of the implementing class — not from a static context.
2. You must use the interface name — not just super.method().

💡 Diamond Problem Example

interface A {
    default void hello() { System.out.println("Hello from A"); }
}

interface B {
    default void hello() { System.out.println("Hello from B"); }
}

class C implements A, B {
    @Override
    public void hello() {
        // Must resolve the conflict manually
        A.super.hello(); // or B.super.hello()
    }
}

✅ Summary

You Want To…	You Do This
Call a default method in implementing class	InterfaceName.super.methodName();
Resolve conflict between multiple interfaces	Explicitly choose which one to call