Book Image

Learning Java Lambdas

By : Toby Weston
Book Image

Learning Java Lambdas

By: Toby Weston

Overview of this book

In this short book, we take an in-depth look at lambdas in Java, and their supporting features. The book covers essential topics, such as functional interfaces and type inference, and the key differences between lambdas and closures. You will learn about the background to functional programming and lambdas, before moving on to understanding the basic syntax of lambdas and what differentiates these anonymous functions from standard anonymous classes. Lastly, you'll learn how to invoke lambdas and look at the bytecode generated. After reading this book, you'll understand lambdas in depth, their background, syntax, implementation details, and how and when to use them. You'll also have a clear knowledge of the difference between functions and classes, and why that's relevant to lambdas. This knowledge will enable you to appreciate the improvements to type inference that drive a lot of the new features in modern Java, and will increase your understanding of method references and scoping.
Table of Contents (10 chapters)

Example 2


The Example 2 class is another anonymous class but this time it closes over the server variable. It's an old style closure:

public class Example2 {
    // anonymous class (closure)
    void example() throws InterruptedException {
        Server server = new HttpServer();
        waitFor(new Condition() {
            @Override
            public Boolean isSatisfied() {
                return !server.isRunning();
            }
        });
    }
}

The bytecode is similar to the previous except that an instance of the Server class is newed up (at line 3.) and it's constructor called at line 5. The instance of the anonymous class $1 is still constructed with invokespecial (at line 11.) but this time it takes the instance of Server as an argument as well as the instance of the calling class.

To close over the server variable, it's passed directly into the anonymous class:

void example() throws java.lang.InterruptedException;
  ...