Functional Interfaces

Java 8 introduced the concept of functional interfaces, interfaces that contains exactly one abstract method. These interfaces are used extensively in lambda expressions, streams and in method references.

To make any interface as Functional Interface then we have to use the following annotation just above the interface @FunctionalInterface. The @FunctionalInterface annotation is used to indicate that an interface is intended to be a functional interface. This annotation is optional but provides compiler-level checks.

Code Example

​x
 
import java.util.*;​@FunctionalInterfaceinterface MyFunctionalInterface {    void myMethod();}​public class MyClass {    public static void main(String[] args) {        MyFunctionalInterface fi = () -> System.out.println("my-method executed");        fi.myMethod();    }}

Output

my-method executed

1: CalculatorDemo

xxxxxxxxxx
 
import java.util.*;​@FunctionalInterfaceinterface Calculator {    int operate(int a, int b);}​public class Main {    public static void main(String[] args) {        // Using a lambda expression        Calculator addition = (a, b) -> a + b;        Calculator subtraction = (a, b) -> a - b;​        System.out.println("Addition: " + addition.operate(5, 3));               System.out.println("Subtraction: " + subtraction.operate(5, 3));     }}

Output

Addition: 8
Subtraction: 2

Functional Interfaces

Output

Java Tutorial

Python Tutorial