How do I create a functional interface in Java?

How do I create a functional interface in Java?

A functional interface in Java is an interface that has exactly one abstract method. You can create one like this:

@FunctionalInterface
public interface MyFunctionalInterface {
    void myMethod();
}

What is the purpose of the @FunctionalInterface annotation?

The @FunctionalInterface annotation is used to indicate that the interface is intended to be a functional interface. It helps the compiler enforce that the interface has only one abstract method.

Can I have multiple default methods in a functional interface?

Yes, a functional interface can have multiple default methods. Default methods provide a way to add new functionality to interfaces without breaking existing implementations.

How do I use a functional interface with lambda expressions?

You can use a functional interface with lambda expressions like this:

MyFunctionalInterface myFunc = () -> System.out.println("Hello, World!");
myFunc.myMethod();