Week-6: Date:
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VISUAL BEANS:
AIM: Create a simple visual bean with a
area filled with a color.
The
shape of the area depends on the property shape. If it is set to true then the
shape of the area is Square and it is Circle, if it is false.
The color of the area should be
changed dynamically for every mouse click. The color should also be changed if
we change the color in the “property window “.
DESCRIPTION:
A Bean is a JavaBeans component.
Beans are independent, reusable software modules. Beans may be visible objects,
like AWT components, or invisible objects, like queues and stacks. A
builder/integration tool manipulates Beans to create applets and applications.
Beans consist of three things:
Ø Events
An event allows your Beans to communicate when
something interesting happens. There are three parts to this communication:
EventObject
Event Listener - (the
sink)
An Event Source (the Bean)
The event source defines when and
where an event will happen. Classes register themselves as interested in the
event, and they receive notification when the event happens. A series of
methods patterns represents the registration process:
public synchronized void addListenerType(ListenerType l);
public synchronized void removeListenerType( ListenerType l);
Ø Properties
Properties define the characteristics of the
Bean. For instance, when examining an AWT TextField for its properties, you will see properties for
the caret position, current text, and the echo character, among others. A
property is a public attribute of the Bean, usually represented by a non-public
instance variable. It can be read-write, read-only, or write-only. There are
four different types of properties:
- Simple - As the name implies, simple properties represent the simplest of the four. To create a property, define a pair of set/get routines. Whatever name used in the pair of routines, becomes the property name
- Indexed - An indexed property is for when a single property can hold an array of values. The design pattern for these properties is:
public void setPropertyName (PropertyType[] list)
public void setPropertyName (
PropertyType element, int position)
public PropertyType[] getPropertyName ()
public PropertyType getPropertyName (int position)
- Bound – A bean that has the bound property generates an event when the property is changed. The event is of type propertyChangeEvent and is sent to objects that previously registered an interest in receiveing such notifications. In order for the notification to happen, you need to maintain a watch list for PropertyChangeEvents via the PropertyChangeSupport class. First, you have to create a list of listeners to maintain:
private PropertyChangeSupport changes =
new PropertyChangeSupport (this);
And then, you have to maintain the
list:
public void addPropertyChangeListener (
PropertyChangeListener p) {
changes.addPropertyChangeListener (p);
}
public void removePropertyChangeListener (
PropertyChangeListener p) {
changes.removePropertyChangeListener (p);
}
- Constrained - Constrained properties are similar to bound properties. In addition to maintaining a list of PropertyChangeListeners, the Bean maintains a list of VetoableChangeListeners. Then, prior to the Bean changing a property value, it asks the VetoableChangeListeners if its okay. If it isn't, the listener throws a PropertyVetoException, which you declare the set routine to throw.
Ø Methods
Bean methods are available for
anyone to call by just making each public. However, you can restrict which
methods are visible to the Bean builder/integration tool by providing a getMethodDescriptors method along with your Bean's BeanInfo. Every
Bean can provide a supporting BeanInfo class to customize a Bean's appearance to an integration
tool.
Procedural Steps to create a
Java-Bean:
1) Creating a
directory- Create a new directory
in C:\beans\demo\sunw\demo with a new
folder name colors
2) Create a java source
file
3)
Compile the java source file
4)
Create a manifest file
colors.mft in the directory called as C:\beans\demo
5)
Create a jar file- to create a
jar file type the following command in the command prompt
jar cfm ..\jars\colors.jar colors.mft
sunw\demo\colors\*.class
6)
Start the BDK
7)
Check whether the colors bean
is placed in toolbox or not.
PROGRAM:
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(100,100);
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);
}
}
}
OUTPUT:
 |
| http://wikibrand.blogspot.in |
 |
| http://wikibrand.blogspot.in |
RESULT:
Thus the colors bean is created successfully.
Program 2:
Visual
Beans (program 2)
Convert.java
package
sunw.demo.convert;
import
java.awt.*;
import
java.awt.event.*;
public
class convert extends Canvas
{
private double dollars=0.0;
private double rupees=0.0;
private double dollarvalue=0.0;
public convert()
{
setSize(100,1000);
}
public double getDollars()
{
return dollars;
}
public void setDollars(double value)
{
this.dollars=value;
}
public void setRupees(double value)
{
this.rupees=value;
}
public double getRupees()
{
return rupees;
}
public void change()
{
dollarvalue= value();
repaint();
}
private double value()
{
return rupees*dollars;
}
public void paint(Graphics g)
{
g.setColor(Color.red);
g.drawString(String.valueOf(dollarvalue),10,10);
}
}
Convert.mf
Name:
sunw/demo/convert/convert.class
Java-Bean: True ( press Enter)
(Carriage
return compulsory)
 |
| http://wikibrand.blogspot.in |
 |
| http://wikibrand.blogspot.in |
Result
Thus the convertion bean is created successfully
Program
3:
package
sunw.demo.colors;
import
java.awt.*;
import
java.awt.event.*;
public
class mouseclick extends Canvas {
public
int count=0;
public
mouseclick() {
addMouseListener(new
MouseAdapter() {
public
void mousePressed(MouseEvent me) {
change();
}
});
setSize(100,100);
}
public
void change() {
count++;
repaint();
}
public
void paint(Graphics g) {
Dimension
d = getSize();
int
h = d.height;
int
w = d.width;
g.setColor(Color.red);
g.fillRect(0,0,100,100);
g.setColor(Color.blue);
g.drawString(String.valueOf(count),50,50);
}
}
Mouseclick.mft
Name:
sunw/demo/colors/mouseclick.class
Java-Bean:
True
Output
 |
| http://wikibrand.blogspot.in |
Result
Thus the Mouse Clicks bean is created
successfully
SOURCE:PVPSIT FOR JNTU
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