Introducing lambda expressions

Java officially supported lambda expressions when Java 8 was released in 2014. Lambda expressions are shorthand implementations for single abstract method (SAM) classes. In other words, they are quick ways to pass functional arguments instead of anonymous classes.

Making a Runnable a lambda

Prior to Java 8, you might have leveraged anonymous classes to implement interfaces, such as Runnable, on the fly as shown in the following code snippet:

public class Launcher {

    public static void main(String[] args) {

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println("run() was called!");
            }
        };

  ...