Developing a Simple Bean Using the BDK

Developing a Simple Bean Using the BDK

Our new component is called the Colors Bean. It appears as either a rectangle or ellipse that is filled with a color. A color is chosen at random when the Bean begins execution. A public method can be invoked to change it. Each time the mouse is clicked on the Bean, another random color is chosen. There is one boolean read/write property that determines the shape.

The BDK is used to lay out an application with one instance of the Colors Bean and one instance of the OurButton Bean. The button is labeled “Change.” Each time it is pressed, the color changes.

Create a New Bean

Here are the steps that you must follow to create a new Bean:

               1. Create a directory for the new Bean.

               2. Create the Java source file(s).

               3. Compile the source file(s).

               4. Create a manifest file.

               5. Generate a JAR file.

               6. Start the BDK.

               7. Test.

Create a Directory for the New Bean

You need to make a directory for the Bean. To follow along with this example, create

c:\bdk\demo\sunw\demo\colors. Then change to that directory.

Create the Source File for the New Bean

// A simple Bean.

package sunw.demo.colors;

import java.awt.*;

import java.awt.event.*;

public class Colors extends Canvas 

{

transient private Color color;

private boolean rectangular;

public Colors() 

{

addMouseListener(new MouseAdapter()

{

public void mousePressed(MouseEvent me) 

{

change();

}

});

rectangular = false;

setSize(200, 100);

change();

}

public boolean getRectangular()

 {

return rectangular;

}

public void setRectangular(boolean flag)

 {

this.rectangular = flag;

repaint();

}

public void change() 

{

color = randomColor();

repaint();

}

private Color randomColor() 

{

int r = (int)(255*Math.random());

int g = (int)(255*Math.random());

int b = (int)(255*Math.random());

return new Color(r, g, b);

}

public void paint(Graphics g)

{

Dimension d = getSize();

int h = d.height;

int w = d.width;

g.setColor(color);

if(rectangular) 

{

g.fillRect(0, 0, w-1, h-1);

}

else 

{

g.fillOval(0, 0, w-1, h-1);

}

}

}

The import statement at the beginning of the file places it in the package named sunw.demo.colors. Recall from Chapter 9 that the directory hierarchy corresponds to the package hierarchy. Therefore, this file must be located in a subdirectory named sunw\demo\colors relative to the CLASSPATH environment variable.

The color of the component is determined by the private Color variable color, and its shape is determined by the private boolean variable rectangular.

The constructor defines an anonymous inner class that extends MouseAdapter and overrides its mousePressed( ) method. The change( ) method is invoked in response to mouse presses. The component is initialized to a rectangular shape of 200 by 100 pixels.

The change( ) method is invoked to select a random color and repaint the component.

The getRectangular( ) and setRectangular( ) methods provide access to the one property of this Bean. The change( ) method calls randomColor( ) to choose a color and then calls repaint( ) to make the change visible. Notice that the paint( ) method uses the rectangular and color variables to determine how to present the Bean.

Compile the Source Code for the New Bean

Compile the source code to create a class file. Type the following:

                                 

                          javac Colors.java

Create a Manifest File

You must now create a manifest file. First, switch to the c:\bdk\demo directory. This is the directory in which the manifest files for the BDK demos are located. Put the source code for your manifest file in the file colors.mft.

          Name: sunw/demo/colors/Colors.class

          Java-Bean: True

This file indicates that there is one .class file in the JAR file and that it is a Java Bean. Notice that the Colors.class file is in the package sunw.demo.colors and in the subdirectory sunw\demo\colors relative to the current directory.

Generate a JAR File

Beans are included in the ToolBox window of the BDK only if they are in JAR files in the directory c:\bdk\jars. These files are generated with the jar utility. Enter the following:

             jar cfm ..\jars\colors.jar colors.mft sunw\demo\colors\*.class

This command creates the file colors.jar and places it in the directory c:\bdk\jars.

Start the BDK

Change to the directory c:\bdk\beanbox and type run. This causes the BDK to start. You should see three windows, titled ToolBox, BeanBox, and Properties. The ToolBox window should include an entry labeled “Colors” for your new Bean.

Create an Instance of the Colors Bean

After you complete the preceding steps, create an instance of the Colors Bean in the BeanBox window. Test your new component by pressing the mouse anywhere within its borders. Its color immediately changes. Use the Properties window to change the rectangular property from false to true. Its shape immediately changes.

Create and Configure an Instance of the OurButton Bean

Create an instance of the OurButton Bean in the BeanBox window. Then follow these steps:

1. Go to the Properties window and change the label of the Bean to “Change”. You should see that the button appearance changes immediately when this property is changed.

2. Go to the menu bar of the BeanBox and select Edit | Events | action | actionPerformed.

3. Move the cursor so that it is inside the Colors Bean display area, and click the left mouse button. You should see the Event Target Dialog dialog box.

4. The dialog box allows you to choose a method that should be invoked when this button is clicked. Select the entry labeled “change” and click the OK button. You should see a message box appear very briefly, stating that the tool is “Generating and compiling adaptor class.”

5. Click on the button. You should see the color change.