Introspection in Java Beans

Introspection:

The Introspector class provides several static methods that support introspection. Of most interest is getBeanInfo(). This method returns a BeanInfo object that can be used to obtain information about the Bean. It has the following syntax:

static BeanInfo getBeanInfo(Class<?> bean) throws IntrospectionException

[dropshadowbox align=”none” effect=”raised” width=”auto” height=”” background_color=”#ffffff” border_width=”1″ border_color=”#dddddd” ]PropertyDescriptor: This class describes a Bean property. It supports several methods that manage and describe properties. For example, you can determine if a property is bound by calling isBound(). To determine if a property is constrained, call isConstrained(). You can obtain the name of property by calling getName().

EventSetDescriptor: This class represents a Bean event. It supports several methods that obtain the methods that a Bean uses to add or remove event listeners, and to otherwise manage events. For example, to obtain the method used to add listeners, call getAddListenerMethod(). To obtain the method used to remove listeners, call getRemoveListenerMethod(). To obtain the type of a listener, call getListenerType(). You can obtain the name of an event by calling getName().

MethodDescriptor: This class represents a Bean method. To obtain the name of the method, call getName(). You can obtain information about the method by calling getMethod(), shown here:

Method getMethod()
[/dropshadowbox]

Program:

import java.awt.*;
import java.awt.event.*;
import java.io.Serializable;
public class Colors extends Canvas implements Serializable 
{
  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);
}
}
}