Learning Java Lambdas

Learning Java Lambdas

By : Toby Weston

Buy this Book

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.

Learning Java Lambdas

Credits

About the Author

www.PacktPub.com

Customer Feedback

Preface

Free Chapter

Introduction

The road to modern Java

Lambdas Introduction

λs in functional programming

Functions vs classes

λ basic syntax

Lambdas in Depth

Functional interfaces

Type inference improvements

Scoping

Converting a method signature

Example 4 (with method reference)

Example 5

Summary

Bytecode

WaitFor

Example 4 (with Method Reference)

Example 5

Customer Reviews

5 star

4 star

3 star

2 star

1 star

Example 5

package jdk8.byte_code;

import static jdk8.byte_code.Server.*;
import static jdk8.byte_code.WaitFor.waitFor;

public class Example5 {

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

Classfile Example5.class
 Last modified 08-May-2014; size 1470 bytes
 MD5 checksum 7dd0f577d4b4b903500264acf9649c30
 Compiled from "Example5.java"
 public class jdk8.byte_code.Example5
 SourceFile: "Example5.java"
 InnerClasses:
   public static #31= #2 of #29; //HttpServer=class jdk8/byte_code/Server$HttpServer of class jdk8/byte_code/Server
   public static final #68= #67 of #70; //Lookup=class java/lang/invoke/MethodHandles$Lookup of class java/lang/invoke/MethodHandles
 BootstrapMethods:
   0: #34 invokestatic java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
 Method arguments:
 #35 ()Ljava/lang/Boolean; // <-- signature and return type of the SAM method to be implemented by the lambda
 #36 invokestatic jdk8/byte_code/Example5.lambda$example$35:(Ljdk8/byte_code/Server;)Ljava/lang/Boolean;
 #35 ()Ljava/lang/Boolean; // <-- signature and return type to be enforced at invocation time
 minor version: 0
 major version: 52
 flags: ACC_PUBLIC, ACC_SUPER
 Constant pool:
 #1 = Methodref            #10.#28   //java/lang/Object."<init>":()V
 #2 = Class                #30       //jdk8/byte_code/Server$HttpServer   
 #3 = Methodref            #2.#28    // jdk8/byte_code/Server$HttpServer."<init>":()V
 #4 = InvokeDynamic        #0:#37    // #0:isSatisfied:(Ljdk8/byte_code/Server;)Ljdk8/byte_code/Condition;
 #5 = Methodref            #38.#39   // jdk8/byte_code/WaitFor.waitFor:(Ljdk8/byte_code/Condition;)V 
 #6 = InterfaceMethodref   #29.#40   // jdk8/byte_code/Server.isRunning:()Ljava/lang/Boolean;
 #7 = Methodref            #41.#42   // java/lang/Boolean.booleanValue:()Z 
 #8 = Methodref            #41.#43   // java/lang/Boolean.valueOf:(Z)Ljava/lang/Boolean; 
 #9 = Class                #44       // jdk8/byte_code/Example5 
 #10 = Class               #45       // java/lang/Object
 #11 = Utf8                <init> 
 #12 = Utf8                ()V 
 #13 = Utf8                Code 
 #14 = Utf8                LineNumberTable 
 #15 = Utf8                LocalVariableTable 
 #16 = Utf8                this 
 #17 = Utf8                Ljdk8/byte_code/Example5; 
 #18 = Utf8                example 
 #19 = Utf8                server 
 #20 = Utf8                Ljdk8/byte_code/Server; 
 #21 = Utf8                Exceptions 
 #22 = Class               #46 // java/lang/InterruptedException 
 #23 = Utf8                lambda$example$35 
 #24 = Utf8                (Ljdk8/byte_code/Server;)Ljava/lang/Boolean;   
 #25 = Utf8                StackMapTable
 #26 = Utf8                SourceFile
 #27 = Utf8                Example5.java
 #28 = NameAndType         #11:#12   // "<init>":()V 
 #29 = Class               #47       // jdk8/byte_code/Server 
 #30 = Utf8                jdk8/byte_code/Server$HttpServer
 #31 = Utf8                HttpServer 
 #32 = Utf8                InnerClasses 
 #33 = Utf8                BootstrapMethods
 #34 = MethodHandle        #6:#48    // invokestatic java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
 #35 = MethodType          #49       // ()Ljava/lang/Boolean; 
 #36 = MethodHandle        #6:#50    // invokestatic jdk8/byte_code/Example5.lambda$example$35:(Ljdk8/byte_code/Server;)Ljava/lang/Boolean; 
 #37 = NameAndType         #51:#52   // isSatisfied:(Ljdk8/byte_code/Server;)Ljdk8/byte_code/Condition; 
 #38 = Class              #53        // jdk8/byte_code/WaitFor 
 #39 = NameAndType        #54:#55    // waitFor:(Ljdk8/byte_code/Condition;)V 
 #40 = NameAndType        #56:#49    // isRunning:()Ljava/lang/Boolean; 
 #41 = Class              #57        // java/lang/Boolean 
 #42 = NameAndType        #58:#59    // booleanValue:()Z 
 #43 = NameAndType        #60:#61    // valueOf:(Z)Ljava/lang/Boolean; 
 #44 = Utf8               jdk8/byte_code/Example5 
 #45 = Utf8               java/lang/Object 
 #46 = Utf8               java/lang/InterruptedException 
 #47 = Utf8               jdk8/byte_code/Server 
 #48 = Methodref          #62.#63    // java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite; 
 #49 = Utf8               ()Ljava/lang/Boolean;
 #50 = Methodref          #9.#64     // jdk8/byte_code/Example5.lambda$example$35:(Ljdk8/byte_code/Server;)Ljava/lang/Boolean;
 #51 = Utf8               isSatisfied
 #52 = Utf8          (Ljdk8/byte_code/Server;)Ljdk8/byte_code/Condition; 
 #53 = Utf8               jdk8/byte_code/WaitFor 
 #54 = Utf8               waitFor 
 #55 = Utf8               (Ljdk8/byte_code/Condition;)V
 #56 = Utf8               isRunning 
 #57 = Utf8               java/lang/Boolean
 #58 = Utf8               booleanValue 
 #59 = Utf8               ()Z 
 #60 = Utf8               valueOf
 #61 = Utf8               (Z)Ljava/lang/Boolean;
 #62 = Class              #65        // java/lang/invoke/LambdaMetafactory 
 #63 = NameAndType        #66:#69    // metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
 #64 = NameAndType        #23:#24    // lambda$example$35:(Ljdk8/byte_code/Server;)Ljava/lang/Boolean;
 #65 = Utf8               java/lang/invoke/LambdaMetafactory 
 #66 = Utf8               metafactory 
 #67 = Class              #71        // java/lang/invoke/MethodHandles$Lookup 
 #68 = Utf8               Lookup
 #69 = Utf8 (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite; 
 #70 = Class              #72        //java/lang/invoke/MethodHandles   
 #71 = Utf8               java/lang/invoke/MethodHandles$Lookup 
 #72 = Utf8               java/lang/invoke/MethodHandles
{
  public jdk8.byte_code.Example5();
   descriptor: ()V
   flags: ACC_PUBLIC
   Code:
     stack=1, locals=1, args_size=1
       0: aload_0
       1: invokespecial #1           // Method java/lang/Object."<init>":()V 
       4: return
    LineNumberTable:
      line 6: 0
    LocalVariableTable:
      Start Length Slot Name Signature
          0      5    0 this Ljdk8/byte_code/Example5;
void example() throws java.lang.InterruptedException;
  descriptor: ()V
  flags:
  Code:
    stack=2, locals=2, args_size=1
       0: new           #2           //class jdk8/byte_code/Server$HttpServer
       3: dup
       4: invokespecial #3           // Method jdk8/byte_code/Server$HttpServer."<init>":()V
       7: astore_1
       8: aload_1

       9: invokedynamic #4,  0       // InvokeDynamic #0:isSatisfied:(Ljdk8/byte_code/Server;)Ljdk8/byte_code/Condition;
       14: invokestatic  #5                  // Method jdk8/byte_code/WaitFor.waitFor:(Ljdk8/byte_code/Condition;)V
       17: return
      LineNumberTable:
        line 10: 0
        line 11: 8
        line 12: 17
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      18     0  this   Ljdk8/byte_code/Example5;
            8      10     1 server   Ljdk8/byte_code/Server;
    Exceptions:
      throws java.lang.InterruptedException
}

Learning Java Lambdas

By : Toby Weston

Learning Java Lambdas

By: Toby Weston

Overview of this book

Related Content you might be interested in

Current Title:

Learning Java Lambdas

Programming Kotlin

Learn Kotlin Programming

Learn Java with Projects

Example 5