Imagine you are building a notification system for a messaging app. Whenever a new message arrives, you want to process it—perhaps by displaying a notification, logging it, or triggering some other action. Instead of hard-coding the response, you decide to use a lambda expression to handle the event, making your system flexible and easy to extend. In this scenario, a lambda can be passed as an event handler to process each new message as it arrives.

package com.example;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.DisplayName;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Consumer;

import static org.junit.jupiter.api.Assertions.*;

public class MainTest {

    @Test
    @DisplayName("handleNewMessage applies lambda to message")
    void testHandleNewMessageLambdaCalled() {
        AtomicReference<String> result = new AtomicReference<>(null);
        String testMessage = "Test message!";
        Consumer<String> consumer = result::set;
        com.example.Main.handleNewMessage(testMessage, consumer);
        assertEquals(testMessage, result.get(), "Lambda should receive the exact message passed to handleNewMessage");
    }

    @Test
    @DisplayName("handleNewMessage works with different messages")
    void testHandleNewMessageDifferentInput() {
        AtomicReference<String> result = new AtomicReference<>(null);
        String testMessage = "Another message";
        Consumer<String> consumer = result::set;
        com.example.Main.handleNewMessage(testMessage, consumer);
        assertEquals(testMessage, result.get(), "Lambda should receive the exact message passed to handleNewMessage");
    }
}

MainTest.java

Master the power of lambda expressions in Java to write concise, expressive, and modern code. This course guides you from the basics of functional interfaces to advanced lambda usage, including real-world applications and best practices.

Learn the fundamentals of lambda expressions, their syntax, and how they fit into Java's type system.

Dive deeper into lambda expressions with method references, composition, and practical applications in collections.

Learn how to write clean, efficient, and maintainable code with lambda expressions in real-world scenarios.

Challenge: Event Handler with Lambda

Solution