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)

Summary


We saw how using an anonymous class will create a new instance and call it's constructor with invokespecial.

We saw anonymous classes that close over variables have an extra argument on their constructor to capture that variable.

And we saw how Java lambdas use the invokedynamic instruction to defer binding of the types and that a special lambda$ method handle is used to actually represent the lambda. This method handle has no arguments in this case and is invoked using invokestatic making it a genuine function.

The lambda was created by the LambdaMetafactory class which itself was the target of the invokedynamic call.

When a lambda has arguments, we saw how the LambdaMetafactory describes the argument to be passed into the lambda. The invokestatic opcode is used to execute the lambda like before. But we also had a look at a method reference used in-lieu of a lambda. In this case, no lambda$ method handle was created and invokevirtual was used to call the method directly.

Lastly, we looked...