Java初学者指南：学习Java 9+基础编程

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"Java for Absolute Beginners (True PDF)" 是一本专为初学者设计的Java编程教程，强调使用Java 9及更高版本的方式学习基础编程概念。本书由Iuliana Cosmina编写，旨在引导完全没有编程背景的读者入门Java编程。通过本书，读者可以了解到Java 9及其后续版本的新特性和改进，掌握编程的基础知识。书中的内容可能包括但不限于以下方面： 1. **Java简介**：介绍Java语言的历史、特点和应用领域，解释为什么Java是学习编程的良好起点。 2. **环境设置**：指导读者如何安装JDK（Java Development Kit）和配置开发环境，如设置PATH变量和使用集成开发环境（IDE）。 3. **基础语法**：讲解Java的基本语法，包括数据类型（如整型、浮点型、字符型和布尔型）、变量、常量、运算符以及控制流程（如条件语句和循环）。 4. **面向对象编程**：深入介绍面向对象编程的概念，包括类、对象、封装、继承和多态，这是Java的核心特性。 5. **方法和函数**：教授如何定义和调用方法，理解函数在程序中的作用和重要性。 6. **数组**：讲解如何创建和操作数组，包括一维和多维数组。 7. **异常处理**：介绍Java的异常处理机制，学习如何使用try-catch块来处理程序运行时可能出现的问题。 8. **字符串和集合框架**：讨论Java的String类以及集合类如ArrayList和HashMap，它们在实际编程中非常常见。 9. **输入/输出流**：解释如何进行文件操作和数据的输入输出，包括使用FileReader、FileWriter以及更高级的IO流。 10. **Java 9及更高版本的新特性**：介绍Java 9引入的模块系统、JShell（REPL，Read-Eval-Print Loop）以及其他改进，帮助读者了解最新的语言发展。 11. **实践项目**：书中可能包含一些小型项目，让读者将所学知识应用于实践中，提高编程技能。这本书对于想要进入IT行业的初学者来说是一份宝贵的资源，它不仅涵盖了Java编程的基础，还注重培养解决问题和逻辑思维的能力。通过阅读和实践，读者将能够逐步建立起坚实的编程基础，为进一步学习更复杂的Java技术和框架打下坚实的基础。

xix

Introduction

Even though I have been writing Java Applications since 2002 I don’t think I’ve ever dived

so deeply into the JVM as I did while writing this book. Most companies I’ve worked

for had their own code base when I joined them, and my work was mostly related to

designing, improving or maintaining one that already existed. It’s like making brownies

when you already have brownie mix. Writing this book has given me the opportunity to

get down to basics and work with basic ingredients—so, making brownies using eggs,

flower, cocoa, milk, and butter.

Java began in 1982 and was created by a handful of people. The most renowned

name linked to the beginning of Java is James Gosling, also known as the father of

Java, the language that is now used on over three billion devices. When Oracle bought

Sun Microsystems, developers were worried about Java’s future, especially since its

main creator quit the company and went on to create what was thought to be Java’s

replacement: Scala. That will probably never happen. Java is still here.

Most banking applications are written in Java and because it is definitely dangerous

and costly to migrate these applications, Java will be here in 50 years, if not more. Java

began by making websites more dynamic and more entertaining, and ended up being

the basis for applications run on ATMs, cashier machines, computers, and mobile

devices. Sure, this would have been more difficult if Java wasn’t cross-platform.

The first Java version was officially released in 1996. Since then, ten more versions

have been released, with the latest one, Java 11, being released on 25th September 2018.

The work on Java 12 has already begun and the early access build is already available.

This book was written with the intention to cover the fundamental elements of the

language and of the JVM, especially the ones introduced in versions 9, 10, and 11.

The book provides a complete overview of the most important Java classes in the JVM,

all wrapped up in a multimodule project that compiles with Java 11 and Gradle 5.

I. Cosmina, Java for Absolute Beginners, https://doi.org/10.1007/978-1-4842-3778-6_1

CHAPTER 1

An Introduction toJava

andIts History

Java is currently one of the most influential programming languages. It all started in

1990, when an American company that was leading the revolution in the computer

industry decided to gather its best engineers together to design and develop a product

that would allow them to become an important player in the new emerging Internet

world. Among those engineers was James Arthur Gosling, a Canadian computer scientist

who is recognized as the “father” of the Java programming language. It would take five

years of design, programming, and one rename (from Oak to Java because of trademark

issues), but finally in 1996, Java 1.0 was released for Linux, Solaris, Mac, and Windows.

You might have the tendency to skip this chapter altogether. But I think it would be

a mistake. I was never much interested in the history of Java. I was using it for work. I

knew that James Gosling was the creator and that Oracle bought Sun, and that was pretty

much it. I never cared much about how the language evolved, where the inspiration

came from, or how one version was different from another. I started learning Java at

version 1.5, and I took a lot of things in the language for granted. So, when I was assigned

to a project running on Java 1.4, I was quite confused, because I did not know why

some of the code I wrote was not compiling. Although the IT industry is moving very

fast, there will always be that one client that has a legacy application. And knowing the

peculiarities of each Java version is an advantage, because you know the issues when

performing a migration.

When I started doing research for this book, I was mesmerized. The history of Java is

interesting because it is a tale of incredible growth, success of a technology, and how a

clash of egos in management almost killed the company that created it. Because even if

Java is the most used technology in software development, it is simply paradoxical that

the company that gave birth to it no longer exists.

System.out.println("Not A");

}

});

}

In this code example, a list of text values is declared; then the list is traversed, and when

a text is equal to "a", the letter "A" is printed in the console; otherwise, "Not A" is printed.

If you are an absolute beginner to programming, this book is for you, especially

because the sources attached to this book make use of algorithms and design patterns

commonly used in programming. So, if your plan is to get into programming and learn

a high-level programming language, read the book, run the examples, write your own

code, and you should have a good head start.

If you already know Java, you can use this book too because it covers the specifics of

Java versions 9, 10, and 11 (the EAP

release).

How This Book Is Structured

The chapter you are reading is an introductory one that covers a little bit of Java history,

showing you how the language has evolved and a glimpse into its future. Also, the mechanics

of executing a Java application are covered, so that you are prepared for Chapter 2. The

next chapter shows you how to set up a development environment and introduces you

to a simple application. In Chapters 3 to 7, the fundamental parts of the language are

covered: packages, modules, classes, objects, operators, data types, statements, streams,

lambda expressions, and so forth. Starting with Chapter 8 more advanced features are

covered such as: interactions with external data sources: reading writing files, serializing/

deserializing objects, testing and creating an interface. Chapter 12 is dedicated fully to the

publish-subscribe framework introduced in Java 9. Chapter 13 covers the garbage collector.

The book is completed by the java-for-absolute-beginners project. This project is

organized in modules (thus it is a multimodule project) that are linked to each other and

must be managed by Gradle. Gradle is something we developers call a build tool, which

is used to build projects. To build a project means transforming the code into something

that can be executed. I chose to use multimodule projects for the books I write because

it is easier to build them, and common elements can be grouped together, keeping the

Early Access Program

Chapter 1 an IntroduCtIon toJava andIts hIstory

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