Functional interface in java

by May 15, 2021 Java

Let’s learn functional interface in java.

Functional interface in java

Functional interface is one kind of an interface which has only one abstract method.

Syntax:

@FunctionalInterface
interface interfacename
{
   // one abstract method
}

NOTE: @FunctionalInterface is an annotation. This annotation is optional.

Before Java 8 an interface had abstract method signature but don’t define the method itself. It’s upto the implementation class to implement the method of interface.

In Java 8 we can write interfaces which have implementation methods. Functional interface is one kind. This is the type of interface which can be used for declaring or defining lambda expression.

We have a new way of marking a specific interface as functional interface. This gives a indication to other developer that this is meant to be a functional interface.

Here’s functional interface example.

@FunctionalInterface
interface HelloWorld
{
   void print();
}
public class FunctionalInterfaceExample
{
   public static void main(String[] args)
   {
      HelloWorld obj = () -> System.out.println("Hello World Java");
      obj.print();
   }
}

Output:

Hello World Java

Also read – interface in java