Java in a Nutshell: A Desktop Quick Reference, 7th Edition.pdf-资料库

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Playlists Java in a Nutshell, Seventh Edition History by Ben Evans and David Flanagan Topics Copyright © 2019 Benjamin J. Evans and David Flanagan. All rights reserved. Tutorials Printed in the United States of America. Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472. Offers & Deals Highlights O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (http://oreilly.com/safari). For more information, contact our corporate/institutional sales department: 8009989938 or corporate@oreilly.com. Settings Editor: Virginia Wilson Support Production Editor: Justin Billing Sign Out Copyeditor: Jasmine Kwityn Proofreader: Rachel Monaghan Indexer: WordCo Indexing Services, Inc. Interior Designer: David Futato Cover Designer: Karen Montgomery Illustrator: Rebecca Demarest December 2018: Seventh Edition Revision History for the Seventh Edition 20181130: First Release See http://oreilly.com/catalog/errata.csp?isbn=9781492037255 for release details. The O’Reilly logo is a registered trademark of O’Reilly Media, Inc. Java in a Nutshell, the cover image, and related trade dress are trademarks of O’Reilly Media, Inc. The views expressed in this work are those of the authors, and do not represent the publisher’s 2Download from www.finelybook.com 7450911@qq.com

views. While the publisher and the authors have used good faith efforts to ensure that the information and instructions contained in this work are accurate, the publisher and the authors disclaim all responsibility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any code samples or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights. 9781492037255 [LSI] 3Download from www.finelybook.com 7450911@qq.com

History Part I. Introducing Java Topics Tutorials Part I is an introduction to the Java language and the Java platform. These chapters provide enough information for you to get started using Java right away: Chapter 1, Introduction to the Java Environment Offers & Deals Chapter 2, Java Syntax from the Ground Up Highlights Chapter 3, ObjectOriented Programming in Java Chapter 4, The Java Type System Settings Chapter 5, Introduction to ObjectOriented Design in Java Chapter 6, Java’s Approach to Memory and Concurrency Support Sign Out 4Download from www.finelybook.com 7450911@qq.com

History Chapter 1. Introduction to the Java Environment Topics Welcome to Java 11. Tutorials Offers & Deals That version number probably surprises you as much as it does us. It seems like only yesterday that Java 5 was the new thing, and yet here we are, 14 years and 6 major versions later. Highlights You may be coming to the Java ecosystem from another language, or maybe this is your first programming language. Whatever road you may have traveled to get here, welcome—we’re glad you’ve arrived. Settings Support Java is a powerful, generalpurpose programming environment. It is one of the most widely used programming languages in the world, and has been exceptionally successful in business and enterprise computing. Sign Out In this chapter, we’ll set the scene by describing the Java language (which programmers write their applications in), the Java Virtual Machine (which executes those applications), and the Java ecosystem (which provides a lot of the value of the programming environment to development teams). We’ll briefly cover the history of the Java language and virtual machine, before moving on to discuss the lifecycle of a Java program and clear up some common questions about the differences between Java and other environments. At the end of the chapter, we’ll introduce Java security, and discuss some of the aspects of Java that relate to secure coding. The Language, the JVM, and the Ecosystem . The Java programming environment has been around since the late 1990s. It comprises the Java language, and the supporting runtime, otherwise known as the Java Virtual Machine (JVM). At the time that Java was initially developed, this split was considered novel, but recent trends 5Download from www.finelybook.com 7450911@qq.com

in software development have made it more commonplace. Notably, Microsoft’s .NET environment, announced a few years after Java, adopted a very similar approach to platform architecture. One important difference between Microsoft’s .NET platform and Java is that Java was always conceived as a relatively open ecosystem of multiple vendors, albeit led by a steward who owns the technology. Throughout Java’s history, these vendors have both cooperated and competed on aspects of Java technology. One of the main reasons for the success of Java is that this ecosystem is a standardized environment. This means there are specifications for the technologies that comprise the environment. These standards give the developer and consumer confidence that the technology will be compatible with other components, even if they come from a different technology vendor. The current steward of Java is Oracle Corporation (who acquired Sun Microsystems, the originator of Java). Other corporations, such as Red Hat, IBM, Amazon, AliBaba, SAP, Azul Systems, and Fujitsu are also heavily involved in producing implementations of standardized Java technologies. TIP As of Java 11, the primary reference implementation of Java is the open source OpenJDK, which many of these companies collaborate on and base their shipping products upon. Java actually comprises several different but related environments and specifications, such as Java Mobile Edition (Java ME), (Java EE). related to when certain features were introduced into the platform. In this book, we’ll only cover Java SE, version 11, with some historical notes 2 1 Java Standard Edition (Java SE), and Java Enterprise Edition We will have more to say about standardization later, so let’s move on to discuss the Java language and JVM as separate but related concepts. What Is the Java Language? Java programs are written as source code in the Java language. This is a humanreadable programming language, which is strictly class based and object oriented. The language syntax is deliberately modeled on that of C and C++ and it was explicitly intended to be familiar to 6Download from www.finelybook.com 7450911@qq.com

programmers coming from those languages. NOTE Although the source code is similar to C++, in practice Java includes features and a managed runtime that has more in common with more dynamic languages such as Smalltalk. Java is considered to be relatively easy to read and write (if occasionally a bit verbose). It has a rigid grammar and simple program structure, and is intended to be easy to learn and to teach. It builds on industry experience with languages like C++ and tries to remove complex features as well as preserving “what works” from previous programming languages. Overall, Java is intended to provide a stable, solid base for companies to develop business critical applications. As a programming language, it has a relatively conservative design and a slow rate of change. These properties are a conscious attempt to serve the goal of protecting the investment that organizations have made in Java technology. The language has undergone gradual revision (but no complete rewrites) since its inception in 1996. This does mean that some of Java’s original design choices, which were expedient in the late 1990s, are still affecting the language today—see Chapters 2 and 3 for more details. Java 8 added the most radical changes seen in the language for almost a decade (some would say since the birth of Java). Features like lambda expressions and the overhaul of the core Collections code were enormously popular and changed forever the way that Java developers write code. Since then, the platform has produced a release (Java 9) that adds a major (and long delayed) feature: the platform modules system (JPMS). With that release, the project has transitioned to a new, much faster release model where new Java versions are released every six months—bringing us up to Java 11. The Java language is governed by the Java Language Specification (JLS), which defines how a conforming implementation must behave. What Is the JVM? The JVM is a program that provides the runtime environment necessary for Java programs to execute. Java programs cannot run unless there is a JVM available for the appropriate hardware and OS platform we wish to execute on. 7Download from www.finelybook.com 7450911@qq.com

Fortunately, the JVM has been ported to run on a large number of environments—anything from a settop box or Bluray player to a huge mainframe will probably have a JVM available for it. Java programs are typically started from a command line like this: java This brings up the JVM as an operating system process that provides the Java runtime environment, and then executes our program in the context of the freshly started (and empty) virtual machine. It is important to understand that when the JVM takes in a Java program for execution, the program is not provided as Java language source code. Instead, the Java language source must have been converted (or compiled) into a form known as Java bytecode. Java bytecode must be supplied to the JVM in a format called class files (which always have a .class extension). The JVM provides an execution environment for the program. It starts an interpreter for the bytecode form of the program that steps through one bytecode instruction at a time. However, production JVMs also provide a runtime compiler that will accelerate the important parts of the program by replacing them with equivalent compiled machine code. You should also be aware that both the JVM and the user program are capable of spawning additional threads of execution, so that a user program may have many different functions running simultaneously. The design of the JVM built on many years of experience with earlier programming environments, notably C and C++, so we can think of it as having several different goals— which are all intended to make life easier for the programmer: Comprise a container for application code to run inside Provide a secure and reliable execution environment as compared to C/C++ Take memory management out of the hands of developers Provide a crossplatform execution environment These objectives are often mentioned together in discussions of the platform. We’ve already mentioned the first of these goals, when we discussed the JVM and its bytecode interpreter—it functions as the container for application code. 8Download from www.finelybook.com 7450911@qq.com

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