Functional Interfaces

Details about functional interfaces in Java.

What is Functional Interface in Java?

• A functional interface is an interface that contains exactly one abstract method.

• It plays a important role in implementing functional style programming.

• Functional interface is usually marked with @FunctionalInterface annotation. While optional, this annotation helps the compiler verify that the interface adheres to the "single abstract method" rule.

• Java's java.util.function package provides several built-in functional interfaces.

Sample Example

Create a custom functional interface and add sample logic in the main application to use the newly created interface

package org.example;

import lombok.extern.slf4j.Slf4j;

@FunctionalInterface
interface Calculator {
    int calculate(int a, int b);
}

@Slf4j
public class Application {
    public static void main(String[] args) {
        // Define a lambda expression for addition
        Calculator addition = Integer::sum;

        // Use the custom functional interface
        log.info("Addition: {}", addition.calculate(5, 3));
    }
}

Execute the program