Java编程语言基础指南

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"《Java编程语言指南》是一本专为初学者设计的Java教材，由Joan Krone、Thomas Bressoud和R. Matthew Kretchmar三位作者撰写，属于Denison University数学与计算机科学系。本书旨在引导读者学习和理解Java编程语言，它在IT行业中占据重要地位。第1章“介绍”首先阐述了编程语言的学习过程，指出编程就像自然语言（如英语、西班牙语或日语）的学习，需要掌握词汇（即编程语言的词汇和语法元素）、语法规则以及语义（如何组合词汇形成有意义的代码）。编程语言的语义并非固定不变，它会根据选择的词汇和语法结构的不同而有所变化。 Java语言作为本书的核心，它的学习包括理解基本概念，如类（Class）、对象（Object）、数据类型、控制结构（如循环和条件语句）、方法（Functions）以及面向对象编程（Object-Oriented Programming，OOP）的概念。Java的特点在于其平台无关性（Platform Independence），通过Java虚拟机（JVM）使得程序可以在各种操作系统上运行，这在现代软件开发中极具价值。此外，书中还会涉及Java的基本编程环境设置，如开发工具（Integrated Development Environments, IDEs）如Eclipse或IntelliJ IDEA的使用，以及如何编写和调试简单的Java程序。对于初学者来说，章节还会涵盖Java的关键特性，如异常处理（Exception Handling）、集合框架（Collections Framework）和泛型（Generics）等，这些都是构建高效、健壮程序的基础。通过《Java编程语言指南》，读者将逐步掌握Java编程的基础技能，并建立起对面向对象编程的理解，为后续深入学习和在实际项目中应用Java打下坚实基础。无论你是希望进入IT行业的新手，还是希望提升现有技能的开发者，这本书都是一个理想的入门资源。"

CHAPTER 1. INTRODUCTION

of the variable milesValue, whose type is double, in a string expression like

this causes the current value of milesValue to be converted to a string, so that

the ﬁnal result is a string argument that can be passed to println.

The remaining lines of the program, lines 22 through 32, repeat the same kinds

of assignments and print statements. Note that it is perfectly ﬁne to reuse variables.

Exercise 1.6 Study the remainder of the ConvertMilesK main method deﬁnition,

looking for the similarities and differences between these remaining sections and

the section discussed.

Exercise 1.7 Modify the ConvertMilesK program to perform conversions for 15K,

25K, 10 miles, and the ofﬁcial marathon distance of 26 miles, 385 yards.

Exercise 1.8 Create a new class called ConvertFtoC to convert between tem-

peratures in Fahrenheit and their corresponding temperatures in Celsius. Convert

the values 80F, 72F, 32F, and 0F. Be sure and use appropriate names for your

variables.

CHAPTER 2. USER INTERACTION

The next line is an assignment statement in which the right hand side is an

expression made up of a method invocation. Unlike the method invocations we

have seen up to this point, the method must return a value and have an associated

data type in order for the assignment statement to follow its prescribed semantics.

Java (J2SE) 5.0

The method consoleIn.nextInt() is deﬁned to retrieve input typed by

the user, convert the user’s keystroke sequence up to the next Enter into an integer,

and return the integer as the value computed by the method. When we invoke

a method, we pass any paramters needed by the method inside the parentheses

following the method name. In this case, there are no arguments, and so we simply

have ‘()’.

The next two lines, lines 20 and 21, of the Java program repeat the process

of prompting the user for an integer and then retrieving the input from the user

through a method invocation and assignment into the variable secondNumber.

Once the two values to be added are stored in the variables firstNumber

and secondNumber, we are ready to compute their sum. This is accomplished

on line 23 with an assignment statement whose target is the variable sum and

whose computation is given by the expression, evaluating the current values of

firstNumber and secondNumber, and adding them together to get a value.

In similar fashion to earlier examples, the value of the variable sum is then

printed out to the console.

Exercise 2.1 We have seen the use of integer variables and the corresponding

methods to retrieve an integer (type int) value as input from the user. We may

also wish to retrieve a double value as input from the user.

Java (J2SE) 5.0

The Scanner class includes a method called nextDouble() for input of a

double value from an object that has type Scanner, such as consoleIn from

the previous example. It is used in exactly the same manner as nextInt().

Create a new application class called AddTwoDoubles that declares the vari-

ables firstNumber and secondNumber and sum to be of type double and

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