How to Build a Minimal New Project in JBuilder 7

English (this page) Greek

Instructions for creating a new project in Java,
with the minimum amount of code needed to make a new applet

Open the JBuilder7 environment (usually done by running  C:\JBuilder7\bin\JBuilderW.exe).

The JBuilder IDE (Integrated Development Environment) opens up.

From the File option of the menu bar (at the top) select [New Project]:

Clicking on [New Project] causes the following dialog to appear:

In the above dialog, the word “untitled1” that originally appears in the Name field has been replaced by the word “Minimal”, which is the name of the project that we will build. In general, we select a name in ASCII characters for our project name (not non-Latin characters, nor with spaces, because the same name will be used for the folder names in which the project will be stored, and JBuilder7 cannot handle non-ASCII letters for folder names). Case sensitivity applies, and it is recommended to use a capital first letter for the name of the project.

In the Template field select “(Default project)” from the drop-down list.

Finally (in that order), go to the Directory field and enter the folder name in which you want your project to be stored. An example is shown in the above figure, assuming the operating system is Windows 7 (which is responsible for the C:/Users part of the folder name), and that the user of the system is called “Harry”. Beyond that point, it is user Harry who decided to organize his folders as shown (“Programs/Java”). The last part of the Directory field is strongly recommended to be identical to the project name (in our case: “Minimal”).

Click on button [Next >], at the bottom of the dialog.

A new dialog appears, which is the second (and final) step in creating a new project. The dialog looks like this:

It is recommended to leave the entries as shown above in this dialog (with the path names adjusted to your computer’s file structure, of course). If you want to know what the roles of the above entries are, here is an explanation:

  • Output path is where the compiled java code goes.

  • Backup path is where JBuilder keeps backups of your source code files.

  • Working directory is the top directory of your project.

  • The path checked as “Default” in the “Source” tab is where your source code files are stored.

  • Finally, the path shown as “Test” is never used.

Click on button [Finish], at the bottom. The main screen of the IDE now shows that we work on project “Minimal”:

From the File option of the menu bar (top) select [New Class]:

Now a new dialog pops up, prompting us to enter the name of the class and other parameters associated with it:

In the “Package” field, the name of the project appears initially in lower case letters. It is recommended to correct the case of the letters so that it corresponds exactly to the way our project was named (“Minimal”).

In the “Class name” field, enter: AppMain

This (“AppMain”) will be the name of the top-level class of our program or applet. Its code will be given below, and will remain virtually unchanged no matter how complex the rest of the project becomes.

Leave the rest of the fields as they are, and click on button [OK]. Now we see the AppMain class in the main window:

The above, shown against black background, is the default code that JBuider7 created for our class “AppMain”. We will fill that with our own code, soon. But first let’s do something about those comments (enclosed in /* and */). We could of course go and modify them now by hand, but if we do that we’ll have changed only the comments of this class (AppMain), and whenever we create a new class the same meaningless comments will be supplied. We can change the default comments once and for all by going to the menu bar and selecting Project and then Project Properties...:

The “Project Properties” dialog will open up, looking a lot like the one we saw at the first step of creating the project. On that dialog, there is a series of tabs at the top. The first tab reads “Paths”, and is the tab we are currently looking at. Click on the next tab, which reads “General”:

We then see what is supplied by default in the comments section of every newly generated class. We can change those values by double-clicking in the empty fields on the right. In the example above, the title “Minimal Project” was entered by hand, as well as the author’s name (“Harry Foundalis”). You should supply your own name.

Clicking on button [OK] brings us back to the AppMain source code. The comments are not changed automatically now (we’d have to change them by hand, thins once only), but we’re ready to enter the proper code for AppMain.

You may now copy the following code and paste into the AppMain editing area, replacing the two lines that define an empty AppMain class. (Copy and paste it as given below, with the spaces between the lines; the spaces are such that when pasted into the JBuilder editor window they will appear normal.)

import java.awt.event.*;
import java.awt.*;
import java.applet.*;

public class AppMain extends Applet {
   static AppFrame frame;
   AppPanel appPanel;
   boolean is_applet;
   public void init() {
      setLayout(new BorderLayout());
      is_applet = true;
      appPanel = new AppPanel (this);
      add ("Center", appPanel);
   public void destroy () {
   public void start () {
   public static void main(String args[]) {
      AppMain appMain = new AppMain();
      appMain.is_applet = false;
      frame = new AppFrame (appMain);

class AppFrame extends Frame implements ActionListener, WindowListener {
   AppMain appMain;
   AppFrame (AppMain _appMain) {
      appMain = _appMain;
      add("Center", appMain);
      setSize (1000, 540);
      addWindowListener (this);
   public void actionPerformed (ActionEvent e) {
      String actionCommand = e.getActionCommand();
   public void windowActivated (WindowEvent e) {}
   public void windowClosed (WindowEvent e) {}
   public void windowClosing (WindowEvent e) {
      setVisible (false);
   public void windowDeactivated (WindowEvent e) {}
   public void windowDeiconified (WindowEvent e) {}
   public void windowIconified (WindowEvent e) {}
   public void windowOpened (WindowEvent e) {}

The above code, as mentioned earlier, will not need to be modified in new projects, save for one point: in the constructor (first method) of the AppFrame class, there is a line that reads: “setTitle("Minimal");”. The word “Minimal” on that line should be changed to whatever the project name is. (That word appears on the title bar of the program.)

Once we paste the above code into the editor window, we see two errors reported on the left-side pane:

The errors read: “Class AppPanel not found” (twice). That’s because we haven’t defined the class AppPanel yet, which is the second important class of our Minimal project.

Before defining the new class AppPanel, we should note that by clicking (once) on each of the errors the IDE shows where the error was detected in the source code. In general, this will be the way we’ll spot out syntax errors in our source code.

Now we’re ready to create the second class of our project, AppPanel. We do that in the same way we created the class AppMain: by selecting File from the menu bar, and then [New Class]:

(Note: this is a repetition of an earlier figure; in your environment the editor window will not be empty but will contain the source code of the AppMain class.)

In the dialog that opens up, we do the following:

We should keep the suggested Package name (“Minimal”), but change the suggested Class name from “Untitled1” to “AppPanel”.

Clicking on [OK] we get the editor window with a default (empty) AppPanel class:

Note that now we see two tabs just above the editor area: one that reads “AppMain” and another that reads “AppPanel”. Each tab has a small button with an X on its left. Clicking on that X closes the tab (we don’t want to close any of them). If the X is incomplete (missing its central region), this is a sign that the source file of that class hasn’t been saved. In the sample figure above, the source of class AppMain has been saved (hence fully drawn X), but the source of class AppPanel is still unsaved (incomplete X). Saving sources is very simple: just under the menu bar there is a row of icons (buttons). The fifth icon shows a floppy disk, and the sixth shows a multitude of them. Clicking on the single-disk icon save the currently edited source file, whereas clicking on the multi-disk icon saves all the unsaved-yet sources (and hence turns all X’s to complete).

Clicking on those tabs is the way we move from one source of our project to another. And if a tab is ever closed by clicking on its X, it can always be recovered by double-clicking on the name of the class, on the left pane of the IDE.

We’re now ready to copy-paste the code of AppPanel, just as we did before for AppMain:

import java.awt.event.*;
import java.awt.*;
import java.applet.*;

public class AppPanel extends Panel implements MouseListener, KeyListener {
   AppMain appMain;                     // the class that creates 'this' class.
   boolean screenPainted;               // flag that controls method Paint().
   Color backgrColor;                   // window background color.

   public AppPanel (AppMain _appMain) {
      appMain = _appMain;
      screenPainted = false;
      backgrColor = Color.white;
      setBackground (backgrColor);

   public void keyPressed (KeyEvent e) {
      if (e.getKeyCode() == KeyEvent.VK_F10) {
         //! Do something if key F10 is pressed, here.
      // Other useful keys:
      // KeyEvent.VK_ENTER
      // KeyEvent.VK_ESCAPE
      // KeyEvent.VK_UP, ...DOWN, ...LEFT, ...RIGHT
   public void keyReleased (KeyEvent e) {}
   public void keyTyped (KeyEvent e) {
      char c = e.getKeyChar();
      if (c == 'A') {
         //! Do something if key 'A' is pressed on the keyboard, here.

   public void mouseClicked(MouseEvent e) { e.consume(); }
   public void mouseEntered(MouseEvent e) { e.consume(); }
   public void mouseExited (MouseEvent e) { e.consume(); }
   public void mousePressed(MouseEvent e) { e.consume(); }
   public void mouseReleased(MouseEvent e) {
      Point point = new Point (e.getX(), e.getY());
      //! Code specifying what happens when clicking anywhere goes here.

   public void paint (Graphics g) {
      int width = getBounds().width;
      int height = getBounds().height;
      if ( ! screenPainted) {
         screenPainted = true;
         //! Code specifying what must happen only once (i.e., initializations)
         //! when the window of the program has just opened, goes here.
      // Code painting things every time the window of the program needs to
      // be painted goes here.

The above code is not exactly minimal, because it contains some template methods that show us how to program things like mouse clicks and key presses on the keyboard. Other than that, however, the code is pretty lean.

Now we should run our progran (which is also an applet, simultaneously). We do this by right-clicking on the word “” shown on the left pane, and then selecting “Run using defaults” from the menu that pops up:

Upon doing that, we see our program/applet running, creating an empty window. The color of the window is white if the variable backgrColor was left initialized with value Color.white in the constructor of class AppPanel. Close the window of our program, go back to the AppPanel source, change the initialization of backgrColor to something like, and run the program again to see its window appearing with a blue background color.

This concludes our first attempt at creating and running a program (and applet) using the JBuilder7 IDE.


Creating project Geometry

Now we’ll use the above project Minimal to create initially a copy of it, which we’ll call “project Geometry”, in which subsequently we’ll add programming code (classes) that will be concerned with simple graphics and notions of geometry.

We’ll start building Geometry initially as a copy of Minimal because we don’t want to “ruin” Minimal. We’ll keep the latter as a template project from which we’ll create, by copying it, every new project that we wish to create.

Exercise: The reader should now be in a position to create the new project Geometry, just as project Minimal was created earlier, following the instructions near the top of this page. That is, select [New Project...] from the menu bar, and then, in the dialog that opens up, enter “Geometry” as project name. Hint: the dialog should look something like this after its fields are filled out with suitable values:

Naturally, the full path names of the folders depend on the organization of folders in the reader’s computer. Note that the file of project Minimal (Minimal.jpx) was given in field Template, which allows the JBuilder IDE to facilitate the creation of the new project.

Click on button [Finish] after filling out the above dialog.

Following the earlier instructions fully, the reader should add the two classes, AppMain and AppPanel, in the new project, run it, and make sure that when it runs it appears exactly as project Minimal. The reader may also substitute the word “Minimal” by the word “Geometry” in the source code of class AppMain.

In what follows we assume that project Geometry exists, and is now a copy of Minimal. Now we’ll add a new class to it: class Circle.

Adding class Circle

Once again we’ll follow the instructions that are already given on this page; specifically here, where it is shown how a new class is added. In the dialog that opens up, we write “Circle” in field Class name, whereas we make sure that “Geometry” (with a capital G) appears in field Package.

It remains to replace the automatically created empty class Circle by the source code given below. This code must be pasted under the initial comments, replacing the existent (empty) class Circle:

import java.awt.*;
import Math.*;
public class Circle {
   // Members:
   Point center;
   int radius;
   Color frame_color, interior_color;
   // Methods:
   public Circle (int cx, int cy, int r) {
      // This is a constructor. What makes it a constructor is
      // its name, which is identical to the name of the class,
      // and the fact that it doesn't have a return type.
      center = new Point();  // here we call the constructor of class Point.
      center.x = cx;
      center.y = cy;
      radius = r;
      frame_color =;  // by default, the circle will be painted with a black circumference
      interior_color = null;      // and with no color in its interior region.
   public double Area () {
      // This is a function that returns the area of 'this' circle, in pixels.
      return Math.PI * radius * radius;     // Math.PI is a predefined constant.
   public void Paint (Graphics g, Color _frame_color, Color _interior_color) {
      // Paints the circle in the colors given as parameters,
      // ignoring the class members 'frame_color' and 'interior_color'.
      // Of course, either or both of the two parameters can be null.
      int x1 = center.x - radius;
      int y1 = center.y - radius;
      int x2 = center.x + radius;
      int y2 = center.y + radius;
      if (_interior_color != null) {
         g.setColor (_interior_color);
         g.fillOval (x1, y1, x2, y2);
      if (_frame_color != null) {
         g.setColor (_frame_color);
         g.drawOval (x1, y1, x2, y2);
   public void Paint (Graphics g) {
      // Paints the circle in the default (member) colors.
      Paint (g, frame_color, interior_color);
   public void SetColors (Color _frame_color, Color _interior_color) {
      if (_frame_color != null)
         frame_color = _frame_color;
      if (_interior_color != null)
         interior_color = _interior_color;