Chapter 1 Introduction to Computers, Programs, and Java

1
Chapter 1Introduction to Computers, Programs,
and Java
2
Objectives

• Review computer basics, programs, and operating
  systems.
• Understand the relationship between Java and the
  World Wide Web.
• Know Javas advantages.
• Understand the terms API, IDE, and JDK.
• Write a simple Java program.

3
Objectives

• Create, compile, and run Java programs
• Understand the Java Runtime Environment (JRE).
• Learn the basic syntax of a Java program.
• To display output on the console and on the
  dialog box.

4
What is a Computer?

• A computer consists of storage devices, memory,
  CPU, communication devices, input devices and
  output devices.

5
How Data is Stored?

• Data 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 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 number
  of adjacent bytes. No two data can share or split
  a same byte.
• A byte is the minimum storage unit.

6
Programs

• Computer programs, known as software, are
  instructions to the computer.
• You tell a computer what to do through programs.
  Without programs or software, a computer is an
  empty machine.
• Computers do not understand human languages, so
  you need to use computer languages to communicate
  with them.
• Programs are written using programming languages.

7
Programming Languages

• Machine language
• is a set of primitive instructions built into
  every computer.
• the instructions are in the form of binary code.
  Program with native machine language is a tedious
  process.
• programs are highly difficult to read and modify.
  For example, to add two numbers, you might write
  an instruction in binary like this
• 1101101010011010

8
Programming Languages

• Assembly languages
• is a low-level language which is
  machine-dependent
• a program called assembler is used to convert
  assembly language programs into machine code.
• For example, to add two numbers, you might write
  an instruction in assembly code (or mnemonic)
• ADDF3 R1, R2, R3

9
Programming Languages

• High-level languages
• are English-like and easy to learn and program.
• For example, the following is a high-level
  language statement that computes the area of a
  circle with radius 5
• area 5 5 3.1415

10
Popular High-Level Languages

• COBOL (COmmon Business Oriented Language)
• FORTRAN (FORmula TRANslation)
• BASIC (Beginner All-purpose Symbolic
  Instructional Code)
• Pascal (named for Blaise Pascal)
• Ada (named for Ada Lovelace)
• 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 (whose developer designed B first)
• Java (We use it in this module)

11
Compiling Source Code

• A program written in a high-level language is
  called a source program.
• A program called a compiler is used to translate
  the source program into a machine language
  program (or called an object program).
• The object program is often then linked with
  other supporting library code before the object
  can be executed on the machine.

12
Compiling Java Source Code

• A source program can be ported to any machine.
• With appropriate compilers, you can compile the
  source program into a special type of object
  code, known as bytecode.
• The bytecode can then run on any computer with a
  Java Virtual Machine (JVM) which interprets Java
  bytecode.
• Java language has the advantage of "Write once,
  run anywhere" (WORA), or "Write once, run
  everywhere" (WORE),

13
Why Java?

• Java enables users to develop and deploy
  applications on
• the internet for web servers,
• desktop computers, and
• small hand-held devices

14
Java, Web, and Beyond

• Java can be used to develop web applications
• Java applets (must be run by a web browser)
• Java servlets and JavaServer Pages (JSP) (must be
  run on a web server)
• Java can also be used to develop applications for
  hand-held devices such as
• Palm, and cell phones

15
Examples of Javas Versatility

• Standalone Application TicTacToe

• Applet TicTacToe

16
Examples of Javas Versatility

• Servlets SelfTest Web site

• Mobile Computing Cell phones

17
Background on Java

• First appeared in 1995
• Developed by Sun Microsystems Corp.
• Cross platform platform-independent
• In May 2007, Sun made available most of their
  Java technologies as free software under GNU
  General Public License.

18
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
• Java Is Multithreaded
• Java Is Dynamic
• www.cs.armstrong.edu/liang/intro6e/JavaCharacteris
  tics.pdf

19
Characteristics of Java

• Java Is Simple
• 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.
• Java Is Object-Oriented
• Object-oriented programming (OOP) is a popular
  programming approach that is replacing
  traditional procedural programming techniques.
• OOP provides great flexibility, modularity,
  clarity, and reusability through encapsulation,
  inheritance, and polymorphism.

20
Characteristics of Java

• Java Is Distributed
• 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
• Java Is Interpreted
• The source programs are compiled into the Java
  Virtual Machine (JVM) code called bytecode.
• The bytecode is machine-independent and can run
  on any machine that has a Java interpreter, which
  is part of the JVM.

21
Characteristics of Java

• Java Is Robust
• Java compilers can detect many problems that
  would first show up at execution time.
• Java has eliminated certain types of error-prone
  programming constructs.
• Java has a runtime exception-handling feature.
• Java Is Secure
• Java implements several security mechanisms to
  protect your system against harm caused by stray
  programs.
• Java Is Architecture Neutral
• Write once, run anywhere (WORA)
• Java Is Portable
• Because it is architecture neutral

22
Characteristics of Java

• Java Is Multithreaded
• Multithread programming is smoothly integrated in
  Java, whereas in other languages you have to call
  procedures specific to the operating system to
  enable multithreading.
• Java Is Dynamic
• Java was designed to adapt to an evolving
  environment.
• New features can be incorporated transparently as
  needed.

23
Java Development Kit (JDK)

• Versions
• JDK 1.5 (2004)
• also called JDK 5 or Java 5 or J2SE 5
• JDK 1.6 (it is the latest version)
• JDK Editions
• Java Standard Edition (J2SE)
• to develop client-side standalone applications or
  applets.
• Java Enterprise Edition (J2EE)
• to develop server-side applications such as Java
  servlets and Java ServerPages.
• Java Micro Edition (J2ME)
• to develop applications for mobile devices such
  as cell phones.
• This module will use J2SE only.

24
Java IDE Tools

• IDE (Integrated Development Environment)
• help programmers to easily edit, compile, build,
  debug Java programs in one graphical user
  interface
• Some Popular Java IDE tools
• Eclipse Open Source by IBM www.eclipse.org
• TextPad Editor www.textpad.com
• NetBeans Open Source by Sun www.netbeans.org
• Sun ONE Studio by Sun MicroSystems
• Borland Jbuilder www.borland.com

25
A Simple Java Program

• Listing 1.1 Welcome.java

//This program prints Welcome to Java! public
class Welcome public static void
main(String args) System.out.println("Wel
come to Java!")
26
Creating and Editing Using Notepad

• To use Notepad, type
• notepad Welcome.java
• from the DOS prompt.

27
Creating, Compiling, and Running Programs
28
Compiling and Running Java from the Command Window

• Set JAVA_HOME environment variable
• set JAVA_HOME"c\Program Files\java\jdk1.5.0"
• Add a search path to JDK bin directory
• set pathpathJAVA_HOME\bin
• Add the current directory to classpath
• set classpath.classpath
• Compile
• javac Welcome.java
• Run
• java Welcome

29
Anatomy of a Java Program

• Comments
• Package (will be introduced later)
• Reserved words
• Modifiers
• Statements
• Blocks
• Classes
• Methods
• The main method

30
Comments

• Styles of comment
• Line comment
• comments are preceded by two slashes (//) in a
  line
• Paragraph or Block comment
• comments are enclosed between / and / in one or
  multiple lines.
• Javadoc comment
• begin with / and end with /
• Compiler will ignore comments.
• Purposes
• to explain the purpose and design of the program
• to skip execution of certain program statements
  which may cause errors

31
Comments

• /
• Class description goes here.
• _at_version 1.10 04 Oct 1996
• _at_author Firstname Lastname
• /
• // This program prints Welcome to Java!
• public class Welcome
• public static void main(String args)
• String testMessage // store greeting words
• / temporarily not to display message
• System.out.println("Welcome to Java!")
• /

32
Reserved Words or Keywords

• are words that have a specific meaning to the
  compiler and cannot be used for other purposes in
  the program
• The URL from Sun shows the listing of Reserved
  Words http//java.sun.com/docs/books/tutorial/java
  /nutsandbolts/_keywords.html
• reserved words are underlined

//This program prints Welcome to Java! public
class Welcome public static void
main(String args) System.out.println("Wel
come to Java!")
33
Reserved Words or Keywords

• Java Keywords
• abstract continue for new switch
• assert default if package synchronized
• boolean do goto private this
• break double implements protected throw
• byte else import public throws
• case enum instanceof return transient
• catch extends int short try
• char final interface static void
• class finally long strictfp volatile
• const float native super while
• Boolean literals (values)
• true false
• Null value
• null

34
Modifiers

• are reserved words which specify the properties
  of the data, methods, and classes and how they
  can be used.
• The URL from Sun shows the listing of Reserved
  Words http//java.sun.com/j2se/1.4.2/docs/api/java
  /lang/reflect/Modifier.html
• Common modifiers you will learn are
• public, private, protected
• static
• final
• abstract

35
Statements

• they represents an action or a sequence of
  actions.
• Every statement in Java ends with a semicolon
  ().
• A compound statement consists of a sequence of
  statements enclosed in a pair of braces .
• A statement can span multiple lines
• A statement is underlined

//This program prints Welcome to Java! public
class Welcome public static void
main(String args) System.out.println("Wel
come to Java!")
36
Blocks

• A pair of braces in a program forms a block
  that groups components of a program.

37
Classes

• a class is a template or blueprint for objects.
• The mystery of the class will continue to be
  unveiled throughout this book.
• For now, though, understand that a program is
  defined by using one or more classes.
• Related classes can also be grouped into a single
  package for easy distribution

38
Methods

• What is System.out.println?
• println is a pre-defined method in the Java class
  library.
• To learn the usage of some predefined Java
  classes or methods
• read the JDK API (Application Programming
  Interface) documentation
• Programmers can create their own methods

http//java.sun.com/reference/api/
39
main Method

• The main method provides the control of program
  flow.
• It is the starting point of program exectuion.
• The main method always looks like this

public static void main(String args)

40
Message Dialog Box

• Listing 1.2 WelcomeInMessageDialogBox.java

import javax.swing.JOptionPane public class
WelcomeInMessageDialogBox public static void
main(String args) JOptionPane.showMessageD
ialog( null , "Welcome to Java!"
, "Display Message" , JOptionPane.INFORMATI
ON_MESSAGE)
41
Message Dialog Box

• showMessageDialog is a method in the JOptionPane
  class.
• With the import statement, the compiler can
• locate the JOptionPane class from imported
  packages
• java.lang package is implicitly imported
• java.lang.System.out.println can be simplified
  to System.out.println
• Without the import statement,
• JOptionPane.showMessageDialog must be written
  asjavax.swing.JOptionPane.showMessageDialog
• To import all classes in the javax.swing package
  
• import javax.swing.

42
Methods Can be Overloaded

• JOptionPane.showMessageDialog(null, x, y,
  JOptionPane.INFORMATION_MESSAGE)
• JOptionPane.showMessageDialog(null, x)
• x parameter is a string for the text to be
  displayed, and
• y parameter is a string for the title of the
  message dialog box.

43
Blank Lines and White Spaces

• White space
• is a set of characters which includes newline,
  space and tab
• is ignored by compiler, but it makes program more
  readable
• This program looks messy, but it can run !

public class Welcome public
static void main(String args)
System.out.println( "Welcome to
Java!")
44
Some Rules for Beginners

• Naming convention
• Class name should be capitalized in each word.
  E.g. WelcomeInMessageDialogBox
• File extensions
• .java for source program
• .class for compiled bytecode file
• Source file name must have the same name of the
  public class declared
• Java is case-sensitive
• Compiler treats main and Main are different