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  • Book Overview & Buying Learning Java Lambdas
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Learning Java Lambdas

Learning Java Lambdas

By : Toby Weston
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Learning Java Lambdas

Learning Java Lambdas

By: Toby Weston
Buy this Book

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 (5 chapters)
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Preface
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What this book covers
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What you need for this book
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Who this book is for
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Conventions
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Reader feedback
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Customer support
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1
1. Introduction
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1. Introduction
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The road to modern Java
2
2. Lambdas Introduction
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2. Lambdas Introduction
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λs in functional programming
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Functions vs classes
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λ basic syntax
3
3. Lambdas in Depth
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3. Lambdas in Depth
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Functional interfaces
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Type inference improvements
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Method references
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Scoping
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Exception handling
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Lambdas vs closures
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Bytecode recap
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Descriptors
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Converting a method signature
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Code examples
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Example 1
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Example 2
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Example 3
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Example 4
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Example 4 (with method reference)
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Example 5
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Summary
4
A. Bytecode
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WaitFor
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Example 1
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Example 2
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Example 3
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Example 4
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Example 4 (with Method Reference)
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Example 5

Example 4 (with method reference)

Interestingly, if we use a method reference instead, the functionality is exactly the same but we get different bytecode.

public class Example4_method_reference {
    // lambda with method reference
    void example() throws InterruptedException {
        waitFor(new HttpServer(), HttpServer::isRunning);
    }
}

Via the call to LambdaMetafactory when the final execution occurs, method_reference results in a call to invokevirtual rather than invokestatic. The invokevirtual opcode is used to call public, protected an package protected methods so it implies an instance is required. The instance is supplied to the metafactory method and no lambda (or static function) is needed at all; there are no lambda$ in this bytecode.

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