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 5


Lastly, example 5 uses a lambda but closes over the server instance. It's equivalent to example 2 and is a new style closure.

public class Example5 {
    // closure
    void example() throws InterruptedException {
        Server server = new HttpServer();
        waitFor(() -> !server.isRunning());
    }
}

It goes through the basics in the same way as the other lambdas but if we lookup the metafactory method in the bootstrap methods table, you'll notice that this time, the lambda's method handle has an argument of type Server. It's invoked using invokestatic (line 9) and the variable is passed directly into the lambda at invocation time.

BootstrapMethods:
    0: #34 invokestatic LambdaMetafactory.metafactory:
            (LMethodHandles$Lookup;
             LString;LMethodType;
             LMethodType;
             LMethodHandle;LMethodType;)LCallSite;
      Method arguments:
        #35 ()LBoolean; // <-- SAM...