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 4


The Example 4 class is another lambda but this time it takes an instance of Server as an argument. It's equivalent in functionality to example 2 but it doesn't close over the variable; it's not a closure.

public class Example4 {
    // lambda with arguments
    void example() throws InterruptedException {
        waitFor(new HttpServer(), (server) -> server.isRunning());
    }
}

Just like example 2, the bytecode has to create the instance of server but this time, the invokedynamic opcode references the test method of type Predicate. If we were to follow the reference (#4) to the boostrap methods table, we would see the actual lambda requires an argument of type HttpServer and returns a Z which is a primitive boolean.

void example() throws java.lang.InterruptedException;
    descriptor: ()V
    flags:
    Code:
      stack=2, locals=1, args_size=1
         0: new #2 // class Server$HttpServer
         3: dup
         4...