Java Programming , Eng.Omar AlNahal

1. Faculty of Engineering & Information Technology
Software Engineering Department
Computer Science [2]
Instructor: Eng.Omar Al-Nahal
Copyright March , 2010
WWW.PALINFONET.COM
Lab 1:
Introduction ; First Java programs
Software Lab

2. Al-Azhar University – Gaza Faculty of Engineering & IT
Java Lab Manual Eng.Omar H. Al-Nahal
Lab 1
Introduction; First Java programs
Software Lab
1. Lab Objectives
In this Lab you will learn:
1. Learn how to install the Java SDK and JCreator IDE
2. Get introductory training on the JCreator IDE
3. Learn how to create Java program with JCreator & BlueJ
4. Compile and Run a Java Program
2. Prior to the Laboratory
Before you come to the lab, you should read about simple java programs instructions in the course and solve
the homework below. You should also read this laboratory exercise in detail. Note that you must solve the
homework.
• Read in book , Chapters 1 & 2 , Sections 1.13, 2.1,2.2,2.3,2.4
• Review the Theoretical Lesson.
3. Learn Java Programming by Examples
The Compilation Process
Figure: From Source Code to Running Program

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Using the JCreator Integrated Development
What is an IDE?
An IDE (Integrated Development Environment) is an application used to aid a programmer in developing
computer applications or programs.
JCreator uses the JAVAC compiler developed by Sun Microsystems TM to compile the Java source code into
Java Byte code. It is just an editor that provides an easy to use editor and debugger for creating Java source
code. In order to create the JAVA byte code you still need to use the Java Compiler developed by Sun
Microsystems TM.
Using JCreator
To use JCreator the program must first be installed on the computer correctly.
Click on the JCreator icon on the desk top ( IF Dialog boxes appear click next and then ok until the
IDE environment window appears). You should then have a window that looks like
Click on File then New then File (You will have a window that looks like Error! Reference source not
found.)
Figure 2

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For Every File in this class you must (These steps are modified each time you create a new File with names and
folders that pertain to each File).
Select an Empty File and Click Next
Figure 3
Provide a Location, Source Path, and Output Path. This should be a folder in your E: drive. You can change
the path for each text box by clicking on the button next to each text box illustrated above.
Give the File a Name1 (Here we are using HelloWorld as the File Name) Be sure that Location, Source and
Output Path have the same folder as the File Name2.
Click Next then Next then Finish
In order to continue you must complete steps 1 through 3 of the Software Development Method found in your
text booki.
Create the first file for your Java program.
Click File then New then File (You should have the window shown in Error! Reference source not found.)
Fill in the name of the file in the Name and Click Finish
Compile the File -> Click Build and then Compile File

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Run File -> Click Build and then Execute File When you execute the program you will have a window that
looks like that in Figure 1
Figure 1
Output Pane with a typical Error
Output Pane Without an Error
File View Pane Package View Pane Output Pane Edit Window

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A Word about the Java Platform
The Java platform consists of the Java application programming interfaces (APIs) and the Java1 virtual
machine (JVM).
Java APIs are libraries of compiled code that you can use in your programs. They let you add ready-made and
customizable functionality to save you programming time.
The simple program in this lesson uses a Java API to print a line of text to the console. The console printing
capability is provided in the API ready for you to use; you supply the text to be printed.
Java programs are run (or interpreted) by another program called the Java VM. If you are familiar with
Visual Basic or another interpreted language, this concept is probably familiar to you. Rather than running
directly on the native operating system, the program is interpreted by the Java VM for the native operating
system. This means that any computer system with the Java VM installed can run Java programs regardless of
the computer system on which the applications were originally developed.
For example, a Java program developed on a Personal Computer (PC) with the Windows NT operating system
should run equally well without modification on a Sun Ultra workstation with the Solaris operating system, and
vice versa.
Setting Up Your Computer
Before you can write and run the simple Java program in this lesson, you need to install the Java platform on
your computer system.
The Java platform is available free of charge from the java.sun.com web site. You can choose between the
Java® 2 Platform software for Windows 98/2000/XP and 7 or for Solaris. The download page contains the
information you need to install and configure the Java platform for writing and running Java programs.
Note: Make sure you have the Java platform installed and configured for your system before you try to write
and run the simple program presented next.
Writing a Program
The easiest way to write a simple program is with a text editor. So, using the text editor of your choice, create a
text file with the following text, and be sure to name the text file ExampleProgram.java. Java programs are case
sensitive, so if you type the code in yourself, pay particular attention to the capitalization.
//A Very Simple Example
class ExampleProgram {
public static void main(String args [ ]){
System.out.println("I'm a Simple Program");
}
}
Here is the ExampleProgram.java source code file if you do not want to type the program text in yourself.
Compiling the Program
A program has to be converted to a form the Java VM can understand so any computer with a Java VM can
interpret and run the program. Compiling a Java program means taking the programmer-readable text in your
program file (also called source code) and converting it to bytecodes, which are platform-independent
instructions for the Java VM.
The Java compiler is invoked at the command line on Unix and DOS shell operating systems as follows:
javac ExampleProgram.java

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Note: Part of the configuration process for setting up the Java platform is setting the class path. The class path
can be set using either the -classpath option with the javac compiler command and java interpreter command,
or by setting the CLASSPATH environment variable. You need to set the class path to point to the directory
where the ExampleProgram class is so the compiler and interpreter commands can find it. See Java 2 SDK
Tools for more information.
Interpreting and Running the Program
Once your program successfully compiles into Java bytecodes, you can interpret and run applications on any
Java VM, or interpret and run applets in any Web browser with a Java VM built in such as Netscape or Internet
Explorer. Interpreting and running a Java program means invoking the Java VM byte code interpreter, which
converts the Java byte codes to platform-dependent machine codes so your computer can understand and run
the program.
The Java interpreter is invoked at the command line on Unix and DOS shell operating systems as follows:
java ExampleProgram
Common Compiler and Interpreter Problems
If you have trouble compiling or running the simple example in this lesson, refer to the Common Compiler and
Interpreter Problems lesson in The Java Tutorial for troubleshooting help.
Code Comments
Code comments are placed in source files to describe what is happening in the code to someone who might be
reading the file, to comment-out lines of code to isolate the source of a problem for debugging purposes, or to
generate API documentation. To these ends, the Java language supports three kinds of comments: double
slashes, C-style, and doc comments.
Double Slashes
Double slashes (//) are used in the C++ programming language, and tell the compiler to treat everything from
the slashes to the end of the line as text.
//A Very Simple Example
class ExampleProgram {
public static void main(String[] args){
System.out.println("I'm a Simple Program");
} }
C-Style Comments
Instead of double slashes, you can use C-style comments (/* */) to enclose one or more lines of code to be
treated as text.
/* These are
C-style comments
*/
class ExampleProgram {
public static void main(String args []){
System.out.println("I'm a Simple Program"); } }
At the command line, you should see:
I'm a Simple Program
Here is how the entire sequence looks in a terminal window:

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Doc Comments
To generate documentation for your program, use the doc comments (/** */) to enclose lines of text for the
javadoc tool to find. The javadoc tool locates the doc comments embedded in source files and uses those
comments to generate API documentation.
/** This class displays a text string at
* the console.
*/
class ExampleProgram {
public static void main(String args []){
System.out.println("I'm a Simple Program");
} }
Class
• Every java program includes at least one class definition. The class is the fundamental component of all
Java programs.
• A class definition contains all the variables and methods that make the program work. This is contained in
the class body indicated by the opening and closing braces.
Braces
• The left brace ( { ) indicates the beginning of a class body, which contains any variables and methods the
class needs.
• The left brace also indicates the beginning of a method body.
• For every left brace that opens a class or method you need a corresponding right brace ( } ) to close the
class or method.
• A right brace always closes its nearest left brace.
main() method
• This line begins the main() method. This is the line at which the program will begin executing.
String args[]
• Declares a parameter named args, which is an array of String. It represents command-line arguments.
System.out.println
• This line outputs the string “I'm a Simple Program!” followed by a new line on the screen.

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Some common escape sequences.
Escape
sequence Description
n Newline. Position the screen cursor at the beginning of the next line.
t Horizontal tab. Move the screen cursor to the next tab stop.
r Carriage return. Position the screen cursor at the beginning of the current linedo not
advance to the next line. Any characters output after the carriage return overwrite
the characters previously output on that line.
Backslash. Used to print a backslash character.
" Double quote. Used to print a double-quote character. For example,
System.out.println( ""in quotes"" );
displays
"in quotes"
Displaying multiple lines with method System.out.printf.
1 // Fig. 2.6: Welcome4.java
2 // Printing multiple lines in a dialog box.
3
4 public class Welcome4
5 {
6 // main method begins execution of Java application
7 public static void main( String args[] )
8 {
9 System.out.printf( "%sn%sn",
10 "Welcome to", "Java Programming!" );
11
12 } // end method main
13
14 } // end class Welcome4
Welcome to
Java Programming!

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Displaying Text in a Dialog Box by using JOptionPane
Although the programs presented in this book thus far display output in the command window, many Java
applications use windows or dialog boxes (also called dialogs) to display output.
For example, World Wide Web browsers such as Netscape or Microsoft Internet Explorer display Web pages
in their own windows. E-mail programs allow you to type and read messages in a window. Typically, dialog
boxes are windows in which programs display important messages to the user of the program.
Class JOptionPane provides prepackaged dialog boxes that enable programs to display windows containing
messages to users—such windows are called message dialogs.
Figure 2.10 displays the string "WelcomentonJava" in a message dialog.
Line 3 indicates that our program uses class JOptionPane from package javax.swing.
This package contains many classes that help Java programmers create graphical user interfaces (GUIs) for
applications. GUI components facilitate data entry by a program's user, and formatting or presenting data
outputs to the user. In method main, line 10 calls method showMessageDialog of class JOptionPane to display
a dialog box containing a message. The method requires two arguments.
The first argument helps the Java application determine where to position the dialog box. When the first
argument is null, the dialog box appears in the center of the computer screen. The second argument is the
String to display in the dialog box.
Method showMessageDialog is a special method of class JOptionPane called a static method. Such methods
often define frequently used tasks that do not explicitly require creating an object. For example, many
programs display messages to users in dialog boxes. Rather than require programmers to create code that
performs this task, the designers of Java's JOptionPane class declared a static method for this purpose. Now,
with a simple method call, all programmers can make a program display a dialog box containing a message. A
static method typically is called by using its class name followed by a dot (.)
Figure 2.10. Using JOptionPane to display multiple lines in a dialog box.
1 // Fig. 3.17: Dialog1.java
2 // Printing multiple lines in dialog box.
3 import javax.swing.JOptionPane; // import class JOptionPane
4
5 public class Dialog1
6 {
7 public static void main( String args[] )
8 {
9 // display a dialog with the message
10 JOptionPane.showMessageDialog( null, "WelcomentonJava" );
11 } // end main
12 } // end class Dialog1

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4. Activities/Exercises
• Write a program TenHelloWorlds.java that prints "Hello, World" ten times.
• Write an application that displays a checkerboard pattern, as follows:
5. Activities/Homework
• Write an application that displays a box, an oval, an arrow and a diamond using asterisks (*), as follows:
• I typed in the following program. It compiles fine, but when I execute it, I get the error
java.lang.NoSuchMethodError: main. What am I doing wrong?
.
** *** ********** ** * **
** *** ** ** ** *** **
** *** ** ** ** ** ** **
** *** ** ** ** ** ** **
***** ** ** ** ** ** **
** *** ** ** ** ** ** **
** *** ** ** ** ** ** **
** *** ** ** *** ***
** *** ********** * *
public class Hello {
public static void main() {
System.out.println("Doesn't execute");
}
}

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6. Web Resources
# The Deitel & Associates home page for Java How to Program, Sixth Edition.
www.deitel.com/books/jHTP6/index.html
# Sun's home page for Java technology. Here you will find downloads, reference guides for developers,
community forums, online tutorials and many other valuable Java resources.
www.java.sun.com/j2se The home page for the Java 2 Platform, Standard Edition.
# The home page for JCreatora popular Java IDE. JCreator Lite Edition is available as a free
download. A 30-day trial version of JCreator Pro Edition is also available.
www.jcreator.com
# The home page for the BlueJ environmenta tool designed to help teach object-oriented Java to new
programmers. BlueJ is available as a free download. www.blueJ.org
# Free Software Online:-
- JDK-V5 Java SE Development Kit
www.palinfonet.com/pin/java/jdkv5.exe
- JCreator – V4 JCreator is a powerful Free IDE for Java
www.palinfonet.com/pin/java/jcpro400.exe
- Java JCreator: Register with the following
Name: mazuki
Serial: MPEXF3-CE2759-WZ9P34-5YFAZW-MQYK1C-89B44V-G30B5E-P8YNJP
# Free Book - Java How to Program, Sixth Edition
www.palinfonet.com/pin/cs3.htm
# Arab Academy for Information Technology
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