java语言程序设计基础篇(第八版)ppt课件第一章.ppt

《java语言程序设计基础篇(第八版)ppt课件第一章.ppt》由会员分享，可在线阅读，更多相关《java语言程序设计基础篇(第八版)ppt课件第一章.ppt（63页珍藏版）》请在三一办公上搜索。

1、1,Chapter 1 Introduction to Computers, Programs, and Java,2,Objectives,To review computer basics, programs, and operating systems (1.2-1.4). To explore the relationship between Java and the World Wide Web (1.5).To distinguish the terms API, IDE, and JDK (1.6).To write a simple Java program (1.7).To

2、display output on the console (1.7).To explain the basic syntax of a Java program (1.7).To create, compile, and run Java programs (1.8). (GUI) To display output using the JOptionPane output dialog boxes (1.9).,3,What is a Computer?,A computer consists of a CPU, memory, hard disk, floppy disk, monito

3、r, printer, and communication devices.,4,CPU,The central processing unit (CPU) is the brain of a computer. It retrieves instructions from memory and executes them. The CPU speed is measured in megahertz (MHz), with 1 megahertz equaling 1 million pulses per second. The speed of the CPU has been impro

4、ved continuously. If you buy a PC now, you can get an Intel Pentium 4 Processor at 3 gigahertz (1 gigahertz is 1000 megahertz).,5,Memory,Memory is to store data and program instructions for CPU to execute. A memory unit is an ordered sequence of bytes, each holds eight bits. A program and its data m

5、ust be brought to memory before they can be executed. A memory byte is never empty, but its initial content may be meaningless to your program. The current content of a memory byte is lost whenever new information is placed in it.,6,How Data is Stored?,Data of various kinds, such as numbers, charact

6、ers, and strings, are encoded as a series of bits (zeros and ones). Computers use zeros and ones because digital devices have two stable states, which are referred to as zero and one by convention. The programmers need not to be concerned about the encoding and decoding of data, which is performed a

7、utomatically by the system based on the encoding scheme. The encoding scheme varies. For example, character J is represented by 01001010 in one byte. A small number such as three can be stored in a single byte. If computer needs to store a large number that cannot fit into a single byte, it uses a n

8、umber of adjacent bytes. No two data can share or split a same byte. A byte is the minimum storage unit.,7,Storage Devices,Memory is volatile, because information is lost when the power is off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actu

9、ally uses them. There are three main types of storage devices:Disk drives (hard disks and floppy disks), CD drives (CD-R and CD-RW), and Tape drives.,8,Output Devices: Monitor,The monitor displays information (text and graphics). The resolution and dot pitch determine the quality of the display.,9,M

10、onitor Resolution and Dot Pitch,The resolution specifies the number of pixels per square inch. Pixels (short for “picture elements”) are tiny dots that form an image on the screen. The resolution can be set manually. The higher the resolution, the sharper and clearer the image is. However, the image

11、 may be very small if you set high resolution on a small screen monitor. PC monitors are usually 15-inch, 17-inch, 19-inch, or 21-inch. For a 15-inch monitor, a comfortable resolution setting would be 640480 (307,200 pixels).,resolution,The dot pitch is the amount of space between pixels. The smalle

12、r the dot pitch, the better the display.,dot pitch,10,Communication Devices,A regular modem uses a phone line and can transfer data in a speed up to 56,000 bps (bits per second). A DSL (digital subscriber line) also uses a phone line and can transfer data in a speed 20 times faster than a regular mo

13、dem. A cable modem uses the TV cable line maintained by the cable company. A cable modem is as fast as a DSL. Network interface card (NIC) is a device to connect a computer to a local area network (LAN). The LAN is commonly used in business, universities, and government organizations. A typical type

14、 of NIC, called 10BaseT, can transfer data at 10 mbps (million bits per second).,11,Programs,Computer programs, known as software, are instructions to the computer. You tell a computer what to do through programs. Without programs, a computer is an empty machine. Computers do not understand human la

15、nguages, so you need to use computer languages to communicate with them. Programs are written using programming languages.,12,Programming Languages,Machine Language Assembly Language High-Level Language,Machine language is a set of primitive instructions built into every computer. The instructions a

16、re in the form of binary code, so you have to enter binary codes for various instructions. Program with native machine language is a tedious process. Moreover the programs are highly difficult to read and modify. For example, to add two numbers, you might write an instruction in binary like this:110

17、1101010011010,13,Programming Languages,Machine Language Assembly Language High-Level Language,Assembly languages were developed to make programming easy. Since the computer cannot understand assembly language, however, a program called assembler is used to convert assembly language programs into mac

18、hine code. For example, to add two numbers, you might write an instruction in assembly code like this: ADDF3 R1, R2, R3,14,Programming Languages,Machine Language Assembly Language High-Level Language,The high-level languages are English-like and easy to learn and program. For example, the following

19、is a high-level language statement that computes the area of a circle with radius 5: area = 5 * 5 * 3.1415;,15,Popular High-Level Languages,COBOL (COmmon Business Oriented Language)FORTRAN (FORmula TRANslation) BASIC (Beginner All-purpose Symbolic Instructional Code) Pascal (named for Blaise Pascal)

20、 Ada (named for Ada Lovelace) C (whose developer designed B first) Visual Basic (Basic-like visual language developed by Microsoft) Delphi (Pascal-like visual language developed by Borland) C+ (an object-oriented language, based on C)C# (a Java-like language developed by Microsoft)Java (We use it in

21、 the book),16,Compiling Source Code,A program written in a high-level language is called a source program. Since a computer cannot understand a source program. Program called a compiler is used to translate the source program into a machine language program called an object program. The object progr

22、am is often then linked with other supporting library code before the object can be executed on the machine.,17,Operating Systems,The operating system (OS) is a program that manages and controls a computers activities. You are probably using Windows 98, NT, 2000, XP, or ME. Windows is currently the

23、most popular PC operating system. Application programs such as an Internet browser and a word processor cannot run without an operating system.,18,Why Java?,The answer is that Java enables users to develop and deploy applications on the Internet for servers, desktop computers, and small hand-held de

24、vices. The future of computing is being profoundly influenced by the Internet, and Java promises to remain a big part of that future. Java is the Internet programming language.Java is a general purpose programming language. Java is the Internet programming language.,19,Java, Web, and Beyond,Java can

25、 be used to develop Web applications.Java AppletsJava Web ApplicationsJava can also be used to develop applications for hand-held devices such as Palm and cell phones,20,Examples of Javas Versatility (Applets),21,PDA and Cell Phone,22,Javas History,James Gosling and Sun MicrosystemsOakJava, May 20,

26、1995, Sun WorldHotJava The first Java-enabled Web browserEarly History Website:,http:/,23,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multi

27、threaded Java Is Dynamic,Companion Website,www.cs.armstrong.edu/liang/intro8e/JavaCharacteristics.pdf,24,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performanc

28、e Java Is Multithreaded Java Is Dynamic,Java is partially modeled on C+, but greatly simplified and improved. Some people refer to Java as C+- because it is like C+ but with more functionality and fewer negative aspects.,Companion Website,25,Characteristics of Java,Java Is Simple Java Is Object-Orie

29、nted Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Java is inherently object-oriented. Although many object-oriented languages began strictly as procedural languages, Java wa

30、s designed from the start to be object-oriented. Object-oriented programming (OOP) is a popular programming approach that is replacing traditional procedural programming techniques. One of the central issues in software development is how to reuse code. Object-oriented programming provides great fle

31、xibility, modularity, clarity, and reusability through encapsulation, inheritance, and polymorphism.,Companion Website,26,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable

32、 Javas Performance Java Is Multithreaded Java Is Dynamic,Distributed computing involves several computers working together on a network. Java is designed to make distributed computing easy. Since networking capability is inherently integrated into Java, writing network programs is like sending and r

33、eceiving data to and from a file.,Companion Website,27,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,You need a

34、n interpreter to run Java programs. The programs are compiled into the Java Virtual Machine code called bytecode. The bytecode is machine-independent and can run on any machine that has a Java interpreter, which is part of the Java Virtual Machine (JVM).,Companion Website,28,Characteristics of Java,

35、Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Java compilers can detect many problems that would first show up at execution time in oth

36、er languages. Java has eliminated certain types of error-prone programming constructs found in other languages. Java has a runtime exception-handling feature to provide programming support for robustness.,Companion Website,29,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Dis

37、tributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Java implements several security mechanisms to protect your system against harm caused by stray programs.,Companion Website,30,Characterist

38、ics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Write once, run anywhereWith a Java Virtual Machine (JVM), you can write one

39、program that will run on any platform.,Companion Website,31,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Becau

40、se Java is architecture neutral, Java programs are portable. They can be run on any platform without being recompiled.,Companion Website,32,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutra

41、l Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Javas performance Because Java is architecture neutral, Java programs are portable. They can be run on any platform without being recompiled.,Companion Website,33,Characteristics of Java,Java Is Simple Java Is Object-Oriented

42、 Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,Multithread programming is smoothly integrated in Java, whereas in other languages you have to call procedures specific to the

43、operating system to enable multithreading.,Companion Website,34,Characteristics of Java,Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Javas Performance Java Is Multithreaded Java Is Dynamic,J

44、ava was designed to adapt to an evolving environment. New code can be loaded on the fly without recompilation. There is no need for developers to create, and for users to install, major new software versions. New features can be incorporated transparently as needed.,Companion Website,35,JDK Versions

45、,JDK 1.02 (1995)JDK 1.1 (1996)JDK 1.2 (1998)JDK 1.3 (2000)JDK 1.4 (2002)JDK 1.5 (2004) a. k. a. JDK 5 or Java 5JDK 1.6 (2006) a. k. a. JDK 6 or Java 6JDK 1.7 (possibly 2010) a. k. a. JDK 7 or Java 7,36,JDK Editions,Java Standard Edition (J2SE)J2SE can be used to develop client-side standalone applic

46、ations or applets.Java Enterprise Edition (J2EE)J2EE can be used to develop server-side applications such as Java servlets and Java ServerPages. Java Micro Edition (J2ME). J2ME can be used to develop applications for mobile devices such as cell phones. This book uses J2SE to introduce Java programmi

47、ng.,37,Popular Java IDEs,NetBeans Open Source by Sun Eclipse Open Source by IBM,38,A Simple Java Program,/This program prints Welcome to Java! public class Welcome public static void main(String args) System.out.println(Welcome to Java!); ,Run,Welcome,Listing 1.1,IMPORTANT NOTE: (1) To enable the bu

48、ttons, you must download the entire slide file slide.zip and unzip the files into a directory (e.g., c:slide) . (2) You must have installed JDK and set JDKs bin directory in your environment path (e.g., c:Program Filesjavajdk1.6.0_14bin in your environment path.,39,Creating and Editing Using NotePad

49、,To use NotePad, type notepad Welcome.java from the DOS prompt.,40,Creating and Editing Using WordPad,To use WordPad, type write Welcome.java from the DOS prompt.,41,Creating, Compiling, and Running Programs,42,Compiling Java Source Code,You can port a source program to any machine with appropriate

50、compilers. The source program must be recompiled, however, because the object program can only run on a specific machine. Nowadays computers are networked to work together. Java was designed to run object programs on any platform. With Java, you write the program once, and compile the source program