ITM 172

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ITM 172

• The Java Programming Language
• Chapter 1 Part A
• Introduction to Java and the Development Tools

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Java Why it is a popular programming language

• Main reason Programs written in Java can run on
  any type of computer.
• A computers processor has an instruction set. (a
  list of all the instructions it understands).
• A Pentium IV processors instruction set is not
  identical to DECs Alpha processors instruction
  set or Suns Sparc processors instruction set.
• Therefore, if you write a program and then
  compile it so that it runs on a Pentium
  processor, it might not run on an Alpha or Sparc
  processor (because the program contains
  instructions that are not in that processors
  instruction set).
• When Java programs are compiled, they can run on
  any type of processor (Therefore, Java programs
  have high portability and are architecturally-neut
  ral).

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The portability of Java programs

• The way that Java programs must be compiled into
  bytecode and then interpreted by the JVM is what
  makes Java programs completely portable.
• Portable means that a Java application can run on
  any hardware/operating system combination.
• Since Java programs are not translated into a
  specific processors machine language until
  runtime, the program can wait until it sees
  what platform it has landed on before it
  finishes compiling. Then it can adapt itself by
  compiling into any specific processors machine
  language at runtime.

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Other advantages of Java

• Simple. Its easier to learn than C
• Object-oriented. Programming code is organized
  into modules/building blocks/objects. Huge
  libraries of these building blocks already
  exist. Programs can be built using standard
  building blocks.
• Distributed. Java programs can interface
  (communicate with) other programs running on
  other computers using standardized communication
  methods.
• Multi-threaded. The Java language allows the
  programmer to write programs that can spawn
  processes simultaneously.

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Other advantages of Java

• Dynamic. Java is an extensible language. That
  means, new functionality can be added
  indefinitely.
• Robust. Java programs dont crash as readily as
  programs written in other languages because the
  compiler does some forward thinking error
  detection and correction.
• Secure. Viruses cannot embed themselves in Java
  programs.

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Java Application Development
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Write Source Code in Java
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java.exe is the VIRTUAL MACHINE
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The Java platform

• In order for an application program to run on a
  computer, certain resources must be available to
  it.
• Resources consists of hardware and software.
  Collectively, these resources are called the
  hosting platform.
• The next slides will explain what a platform is,
  and then what platform Java applications require.

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What is a computer platform?

• In computing, a platform describes all the
  hardware and software programs that must be
  available (as resources) in order for an
  application to run.
• Example A personal computer (complete with a CPU
  and a RAM memory) running the Windows Vista
  operating system.
• Example A high-end computer (multiple
  processors, many GBs of RAM) running the Unix
  operating system.

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What does the platform provide?

• The application program cannot carry out all
  computing tasks on its own without help from
  other programs (we call services) that are
  included in the operating system software package
  and the hardware.
• For example, Microsoft Word cannot carry out all
  the word processing tasks (such as printing,
  saving and opening files, etc.) without the help
  of the operating systems helper programs (some
  may be in .dll files) and the hardware (CPU, RAM,
  disk drive, printer).

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The Java Platform

• A Java application cannot execute unless it is
  running on a computer hosting the Java platform.
• The Java platform consists of these components
  that must be available at runtime the hardware,
  the operating system, and the JRE (the Java
  runtime environment).
• Non-Java applications only need two components in
  their platform the hardware and the operating
  system.

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The Java Platform

• So, to run a Java application, there must be
• Hardware (a CPU, RAM, etc.)
• an operating system
• The JRE
• a. the JVM (the byte code interpreter and the
  program launcher)
• b. the class library (helper modules similar to
  .dll files that augment the functionality of the
  operating system).

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JRE Part A The JVM (Java Virtual Machine)

• The JVM consists of two things it uses its
  interpreter to translate the byte code into
  machine language and it uses its launcher to
  initiate the running of the application.
• The JVMs interpreter is the program that
  completes the translation process by translating
  the byte code into a specific processors machine
  language.

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JRE Part BThe class library

• The other component of the JRE is the class
  library (aka API - Application Programming
  Interface)
• The API is a large collection of reusable
  modules of code. Many of the modules in this
  library are used like .dll files providing
  helper programs that augment the functionality
  of the operating system.

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Java Development Tools

• We just finished discussing what resources are
  needed to run a Java application.
• Now we will discuss what resources are available
  to develop a Java application.
• These resources are called tools
• The JDK (Java Development Kit)
• An IDE (NetBeans)

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The Java Development Toolkit (JDK)

• To create, compile, and run a Java program, you
  need a program called the Java Development
  Toolkit (JDK). The toolkit includes
• javac The compiler, which converts source code
  into Java bytecode
• jar The archiver, which packages related class
  libraries into a single file (similar to a zip
  program).
• javadoc The documentation generator, which
  automatically generates documentation from source
  code comments
• jdb The debugger
• JRE (for testing purposes)

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The Integrated Development Environment (IDE)

• The IDE is like the dashboard of your car it
  makes several programming tools accessible from
  one integrated, GUI-style screen.
• These tools include the text editor, compiler,
  run-time module, debugger, and help system. The
  IDE also forces you to organize your files into
  projects and packages.
• The name of our IDE is NetBeans. (Other products
  that are IDEs include Forte by Sun, Jbuilder by
  Borland, Visual J by Microsoft, Visual Café by
  WebGain).

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If you want to download and install the JDK and
the IDE (Netbeans) on your home computer, go to
www.java.sun.com and select this link.
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Download this version. On the next link, select
the Windows platform (not Linux or Solaris).
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Getting started (Lab 1)

• The JDK version J2SE 6.3 (containing the JRE) and
  Netbeans 6.0 have already been installed on your
  PC.

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Lab 1.1- Part A - Class Welcome in Package
Chapter1

• This program displays the message Welcome to
  Java on the screen (in the standard output
  window not in a Windows window).

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Start the IDE (NetBeans) From the Windows
desktop, click Start, Programs, NetBeans
6.3, NetBeans IDE
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See the NetBeans window.
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If you use NetBeans, all programs must be
encapsulated in a project. A project folder is
created and default settings are applied to the
project folder. To create a project, from the
menu, click File, New Project
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chose General for the project category and
Java Application for the type of project. Click
Next
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Type the Project Name Welcome Type the Project
Location C\251lastnameLABS Unselect Create
Main Class. Click Finish.
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See the project name appear in the Projects
panel. At least two folders are created below the
projects folder. Click the to expand the
Welcome project folder, and then click the
to expand the Source Packages folder. Just as a
project is a container for an application, a
package is a container (also a folder) for a
collection of similar files within a project.
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All Java code must be encapsulated in class
files. Therefore, the next step is to create a
class/file. From the menu, select File, New
File
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in the New File window, click Java Classes
as the Category and Java Main Class as the file
type. Click Next
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welcome
type the class name Welcome (same as the
project name). Type the package name welcome.
Click Finish.
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The class structure
The main method structure
A file is created that contains some startup
code. It opens in the text editor window. A class
structure is created (with the class name
Welcome) and a method is created (with the name
main).
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Type your name and the lab number in the comment
area in the top. Delete everything except what
you see in this screen shot.
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To create our first Java program, that displays
the words, Welcome to Java, type in method
main System.out.println(Welcome to Java)
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To compile the program, from the menu, select
Build, Compile Welcome.java or press F9.
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The output window shows if you have any syntax
errors. If not, you will see the message BUILD
SUCCESSFUL.
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To run the program, from the menu select Run,
Run other, Run Welcome.java or press Shift-F6.
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When the program runs, you will see the message
Welcome to Java appear in the output window.
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Minimize the NetBeans application window to view
the Windows desktop. Click on Folders view on
the toolbar. Navigate to the source file that you
created. It is under Local Disk C,
251lastnameLABS, Welcome, build, classes,
welcome. See one file Welcome.class
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Restore the NetBeans window so you can exit the
program.
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Anatomy of a Java Program

• Programming statements are grouped into methods.
• Methods and variables are grouped into classes.
• Each class is stored in its own unique file with
  the same name as the class.
• Files are grouped into packages
• Packages are grouped into projects.

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System.out.println

• To display a line of text on a computer screen,
  we invoked the pre-existing method println( ).
• When you want your program to display a string of
  text in the standard output window, invoke the
  println method and pass it the string you want
  displayed (Welcome to Java).
• The println( ) method is method belonging to the
  outstream class, and out is an instance of an
  outstream. out is declared in the System class.
• The System class is in the java.lang package,
  which is in the API (the collection of class
  files included in the JRE). Recall that the JRE
  contains a collection of helper modules that
  can be called upon to perform certain processes
  on behalf of your program.

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Comments

• Lines that begin with // or multiple lines
  enclosed in / . /
• Example
• // This is a comment.
• / This is also a comment. /
• Comments are ignored by the compiler.

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Reserved Words

• Reserved or key words have special meaning to the
  compiler and cannot be used for other purposes in
  a program
• Example words like class, package, public, main,
  static, void.

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Modifiers

• Modifiers are key words that specify properties
  of data, methods, and classes. For example, the
  key word public specifies whether other methods
  may invoke the methods and/or access the data
  (variables that are) declared in this class.

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Blocks

• A pair of curly braces form a block. There
  are class blocks, method blocks, and if blocks,
  while blocks, etc.

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The main( ) method

• All executable classes must contain a method
  named main( ).
• Main( )will be the first method invoked when a
  class (or an instance/object of that class) is
  loaded into memory.
• Because main( ) is method, it must have a header
  and a body. Its header looks like this
• public static void main(String args)
• Later, this will make more sense to you.

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Lab 1.1 Part B modify class Welcome in
Package Chapter1

• In this program, we simply modify the way we
  display the output.
• The output of this program is a text string
  Welcome to Java.
• Instead of displaying the string in the standard
  output window, well display it in a
  messageDialog box.

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Using GUI objects in a Java Program

• If you dont specify otherwise, the output
  (Welcome to Java) of a Java program (such as
  Welcome.java) will display in the standard
  output window.
• Modern day programs generally display their
  output in a Windows window called a GUI (Graphic
  User Interface) component. An example of a GUI
  component that might be used to display output is
  a message dialog box.
• We will modify Welcome.java so that its output
  displays in a message dialog box instead of the
  standard output window.

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Start the IDE (NetBeans) From the Windows
desktop, click Start, Programs, NetBeans
6.0, NetBeans IDE
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welcome
The last file that we edited should display in
the editing window. (If not, click File, Open
Project.
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Edit the file Welcome.java as indicated.
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To compile the program, from the menu, select
Build, Compile Welcome.java or press F9.
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The output window shows if you have any syntax
errors. If not, you will see the message BUILD
SUCCESSFUL.
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To run the program, from the menu select Run,
Run other, Run Welcome.java or press Shift-F6.
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When the program runs, you will see the message
Welcome to Java appear in the Message Dialog
window.
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The window title is Example 1.2 output
The text string is Welcome to Java
The INFORMATION MESSAGE icon.
Click the ok button to dismiss the dialog box.
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JOptionPane.showMessageDialog( )

• When method showMessagedialog( ) is invoked, it
  displays a dialog box on the screen. (A dialog
  box is one type of GUI component).
• showMessageDialog( ) is a method of static class
  JOptionPane, therefore, to invoke this method, we
  use the format classname.methodname
• JOptionPane.showMessageDialog()
• Method showMessageDialog( ) requires 4 arguments
  
• Null means none. (This argument wont be
  explained now.)
• Text to be displayed Welcome to Java
• Title of box Example 1.2 output
• Type of icon to display in the box
  INFORMATION.MESSAGE

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Import javax.swing.JOptionPane

• If you want your program to invoke an external
  method (method showMessageDialog( )), the class
  that the method belongs to (class JOptionPane)
  must be included (imported) into your program.
• Import statements must include the package
  name. Class JOptionPane is in package
  javax.swing (like most of the other GUI component
  classes).
• Where class System (in the Java.lang package) is
  automatically imported into every Java program,
  class JOptionPane is not implicitly imported it
  must be explicitly imported.

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System.exit(0)

• exit( ) is another method that belongs to class
  System.
• Since System is a static class, we use the format
  classname.methodname to invoke method exit( ).
• Method System.exit( ) terminates the program. You
  should explicitly terminate a program so that all
  threads spawned by your program will be
  terminated.
• Method System.exit( ) take a single integer
  argument (0). The zero is used as a signal to
  indicate to the operating system that the program
  terminated normally.