Java9入门指南：初学者编程基础

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"Apress.Java.for.Absolute.Beginners-Java9" 是一本面向初学者的Java编程教程，专注于介绍Java 9及以后版本的基础编程概念。在本书中，作者Iuliana Cosmina旨在帮助完全没有编程背景的人士掌握Java语言的核心概念。Java是一种广泛应用的面向对象的编程语言，广泛用于开发各种软件应用，包括桌面应用、移动应用（尤其是Android平台）以及大型企业级系统。 Java 9是Java的重要更新版本，引入了模块化系统（Project Jigsaw）等新特性，增强了语言的可维护性和性能。书中可能会涵盖以下关键知识点： 1. **基础语法**：讲解Java的基本语法，如变量、数据类型、运算符、流程控制（条件语句和循环）、方法定义和调用。 2. **面向对象编程**：介绍类、对象、封装、继承和多态等面向对象编程的核心概念，这是Java编程的核心。 3. **异常处理**：学习如何处理程序运行时可能出现的错误，通过try-catch语句捕获并处理异常。 4. **集合框架**：介绍ArrayList、LinkedList、HashMap等集合类的使用，以及泛型的概念。 5. **IO流**：讲解输入输出流的使用，包括文件操作和网络通信。 6. **多线程**：理解并发编程，如何创建和管理线程，以及同步和互斥的概念。 7. **模块系统**：Java 9的新特性，如何使用模块化来组织和管理代码，提高系统的可维护性和安全性。 8. **JShell（REPL）**：Java 9引入的交互式命令行工具，用于快速测试代码片段，方便学习和调试。 9. **API和库的使用**：介绍如何使用Java标准库和其他第三方库，例如进行日期时间操作的java.time包。 10. **编译与运行**：学习如何使用JDK中的javac编译器和java运行时环境。 11. **调试与测试**：理解如何使用调试工具进行问题排查，并学习单元测试的重要性。 12. **Java开发工具**：如IntelliJ IDEA或Eclipse等集成开发环境的使用。 13. **最佳实践**：提供编写高效、可读性强的Java代码的指导原则。 14. **实战项目**：通过实际项目让读者将所学知识付诸实践，增强编程技能。这本书适合对编程感兴趣，想要从零开始学习Java的读者，通过学习，他们可以具备编写简单Java程序的能力，并为进一步深入学习Java高级特性和框架打下坚实基础。

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

剩余622页未读，继续阅读

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