Download INTRODUCTION TO BLUEJ

INTRODUCTION TO BLUEJ
by Edward McDowell
BlueJ is a simple integrated development environment for Java created at Monash University and
the University of Southern Denmark for use in teaching elementary computer programming. It is
free and easy to use. BlueJ and its documentation may be downloaded from the BlueJ web page
http://www.bluej.org. The current version of BlueJ requires that the Sun Java Development Kit
J2SE 1.3 or higher be installed on your computer. This is available at the Java web page
http://java.sun.com.
ENTERING BLUEJ
This introduction assumes that you already have BlueJ installed on your computer. The
standard installation creates shortcuts to BlueJ on your desktop and in the
"Start:Programs" menu. Use one of these shortcuts to enter BlueJ. (The first time you
enter BlueJ you may be asked to specify which version of the Java Development Kit to
use with BlueJ. Select a version from the list and click the Launch BlueJ button. If no version of
the JDK is listed, click the "Advanced" button and then "Search drives for Java" to search the
computer thoroughly for the JDK.)
CREATING A PROJECT
You must create a project for each program that you write. Select "Project:New Project" from the
BlueJ menu. A dialog box will open. Enter the name you want for the project folder in the File
Name box and click the Create button. (Specify A:\Hello, for example, to create a project named
Hello on the floppy disk in drive A.) This displays a project window for the new project. The
title bar at the top of the BlueJ window displays the name that you gave to the project. The
project window contains one icon (of a page of paper). You may double click this icon to edit a
project documentation file. (Click the close button to leave the editor. The edited file will be
saved.)
CREATING A CLASS
Click the New Class button to the left of the project window to create a new Java class. A dialog
box will open. Enter the name of the class in the Class Name box. Check the appropriate radio
button in the Class Type box: the choices are Class, Abstract Class, Interface, and Applet. Class
is the correct choice for a standard Java class. Click OK. An icon for the new class will appear in
the project window. Double click this icon to edit the class. Click the close button to leave the
editor. The edited file will be saved.
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COMPILING THE PROJECT
Click the Compile button to the left of the project window to compile every class displayed in
the project window. This translates your classes into the Java bytecode needed to run the
program. If the compilation is successful, "Compiling... Done" will be displayed in the status line
at the bottom of the BlueJ window.
If a class contains an error, an editor window will open and the line where the error was detected
will be highlighted. An error message is displayed in a small window under the editor window.
Locate and fix the error, close the editor, and compile again.
RUNNING THE PROGRAM
To run an application, right click the icon for the class containing the main method. Select "void
main(args)" from the menu. A dialog box will open allowing you to pass strings to the args
parameter. Just click OK. The program will run in a terminal window. (EXIT_ON_CLOSE Bug:
If you use BlueJ 1.2.2 with recent versions of Java, the program will terminate if you call the
JFrame method setDefaultCloseOperation with an argument of JFrame.EXIT_ON_CLOSE. This
may be fixed by specifying JFrame.DISPOSE_ON_CLOSE.)
To run an applet, right click the class that extends Applet. Select "Run Applet" from the menu.
A dialog box will open. Select "Run Applet in appletviewer". Specify the width and height of the
applet in pixels. Click the OK button. The applet will run in the Sun appletviewer. Close the
applet- viewer window to exit the applet.
BREAKING A LOOP
Sometimes a program will hang in an infinite loop. To break the loop select "View:Show
Debugger" from the BlueJ menu. A debugger window will open. click the Halt button at the
lower left corner of the debugger window, click the Terminate button at the lower right corner,
and close the debugger window.
CLOSING A PROJECT
Select "Project:Close" from the BlueJ menu to close the current project. Always close the project
before removing your diskette or exiting BlueJ. Exit BlueJ with "Project:Quit".
OPENING AN EXISTING PROJECT
It is often necessary to open a project that you started earlier. To open an existing project, select
"Project:Open Project" from the BlueJ menu. Enter the name of the project folder, for example
A:\Hello, in the File Name box and click the Open button.
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