Java编程入门指南：从基础到专业实践

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"《Java编程入门指南》是一本由 Roy W. Miller 编著的面向初学者的Java编程教材。该书以英文编写，不仅有助于提升编程技能，还能作为英语学习者的练习材料。作者以其专业背景，来自IBM，确保了内容的专业性和实用性。出版日期为2004年11月19日。本书旨在让读者深入了解Java语言的基本语法和核心概念，包括面向对象编程（Object-Oriented Programming, OOP）及其在Java中的应用。作者引导读者掌握Java编程的基础，涉及的主题广泛，如：OOP原则、Java语言的语法和用法、创建对象、添加行为、操作集合、处理错误以及编写高效代码的技巧。教程分为多个部分，第一部分首先介绍了教程的目的，即通过学习Java语言的面向对象特性，帮助读者建立起Java编程的基础，并明确表示，尽管整个Java平台是一个庞大主题，但这本教程将为初学者提供足够的基础知识，后续的进阶教程则会进一步深化内容，指导读者在Java编程道路上更上一层楼。尽管Java语言在其发展中存在支持者和批评者，但它对软件开发行业的影响力不容忽视。通过阅读这本书，读者不仅能掌握一门重要的编程语言，还能了解到它如何改变并塑造现代软件开发实践。对于希望进入IT领域或者提升现有Java技能的读者来说，这是一本不可或缺的入门宝典。"

However, the Java language also gives every OO programmer the tools necessary

to follow all of the OO rules and produce very good OO code. But doing so requires

discipline. The language doesn't force you to do the right thing.

While many object purists rightfully dispute whether the Java language is OO or not,

this isn't really a productive argument to have. The Java platform is here to stay.

Learn how to do OOP as well as possible with Java code, and leave the purity

arguments to others. The Java language will let you write clear, relatively concise,

and maintainable programs, which is good enough in my book for most professional

situations.

Section 4. The Java language under the covers

How the Java platform works

When you write code in the Java language, like many other languages, you write

source code, then you compile it; the compiler checks your code against the syntax

rules of the language. The Java platform adds another step beyond that, though.

When you compile Java code, you end up with bytecodes. The Java virtual machine

(JVM) then interprets those bytecodes at runtime -- that is, when you tell Java to run

a program.

In file terms, when you write code, you create a .java file. When you compile that file,

the Java compiler creates a .class file, which contains bytecodes. The JVM reads

and interprets that file at runtime, and how it does so is based the platform you're

running on. To run on different platforms, you have to compile your source code

against libraries specific to that platform. As you might imagine, the promise of Write

Once, Run Anywhere ends up being Write Once, Test Anywhere. There are subtle

(or not-so-subtle) platform differences that might make your code behave differently

on different platforms.

Garbage collection

When you create Java objects, the JRE automatically allocates memory space for

that object from the heap, which is the big pool of memory available on your

machine. The runtime then keeps track of that object for you. When your program

isn't using it anymore, the JRE gets rid of it. You don't have to worry about it.

If you've written any software in the C++ language, which is (arguably) OO as well,

you know that as a programmer you have to allocate and deallocate memory for

your objects explicitly by using functions called malloc() and free(). That is

onerous for programmers. It's also dangerous, because it allows memory leaks to

sneak into your programs. A memory leak is nothing more than your program

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Introduction to Java programming

gobbling up memory at an alarming rate, which stresses the processor of the

machine it's running on. The Java platform keeps you from having to worry about

this at all, because it has what's known as garbage collection.

The Java garbage collector is a background process that gets rid of objects that

aren't being used anymore, rather than forcing you to do that explicitly. Computers

are good at keeping track of thousands of things, and at allocating resources. The

Java platform lets the computer do that. It keeps a running count of references to

every object in memory. When the count hits zero, the garbage collector reclaims

the memory used by that object. You can manually invoke the garbage collector, but

I've never had to do so in my career. It usually handles itself, and certainly will for

every coding example in this tutorial.

IDEs versus command-line tools

As we noted before, the Java platform comes with command-line tools that let you

compile ( javac ) and run ( java ) Java programs. So why use an IDE like

Eclipse? Simply because using the command-line tools can be a pain in the neck for

programs of any complexity. They're there for you if you need them, but using an

IDE is most often the wiser choice.

The primary reason this is true is that an IDE manages files and paths for you, and

has wizards that assist you when you want to change your runtime environment.

When I want to compile a Java program with the javac command line tool, I have to

worry about setting the CLASSPATH environment variable ahead of time so that the

JRE can know where my classes are, or I have to set that variable at compile time.

In an IDE like Eclipse, all I have to do is tell Eclipse where to find my JRE. If my

code uses classes that I didn't write, all I have to do is tell Eclipse what libraries my

project references and where to find them. That is far simpler than using the

command line to type in heinously long statements that specify the classpath.

If you want or need to use the command-line tools, you can find out more about how

to use them at Sun's Java Technology Web site (see Resources ).

Section 5. OOP with Java technology

Introduction

Java technology covers a lot, but the language itself isn't huge. Covering it in

English, however, is no small task. This section of the tutorial will not cover the

language exhaustively. Instead, it will cover what you need to know to get started,

and what you're most likely to encounter as a beginning programmer. Other tutorials

(see Resources for pointers to some of them) cover various aspects of the language,

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Introduction to Java programming

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