I have the following source code to consider:

import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.Icon;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.UIManager;

public class vtcSlider extends JComponent
{
    public vtcSlider()
    {
	this(0, 0, 100);
    }

    public vtcSlider(int orientation)
    {
	this(orientation, 0, 100);
    }

    public vtcSlider(int min, int max)
    {
	this(0, min, max);
    }

    public vtcSlider(int orientation, int min, int max)
    {
	super();
	_slider = new JSlider(orientation);
	_icon = UIManager.getIcon("Slider.horizontalThumbIcon");

	setLayout(null);
    }
    
    public void paint(Graphics g)
    {
	_icon.paintIcon(_slider, g, 0, 0);

	// Why can't I do the following instead?
	// _icon.paintIcon(this, g, 0, 0);
    }
    
    public static void main(String[] args)
    {
	JFrame frame = new JFrame();

	vtcSlider slider = new vtcSlider();

	frame.getContentPane().add(slider);
	frame.pack();
	frame.setVisible(true);
    }

    //
    // Public data member section
    //

    //
    // Private data member section
    //
    private JSlider
	_slider;

    private Icon
	_icon;
}

What I wanted to do is to reuse the HorizontalSliderThumbIcon class
from one of the xxxIconFactory (xxx can be Metal, Motif, or Windows).
I can get an instance of this class by using the UIManager.getIcon(String)
method.  However, to draw this icon I would have to pass an
instance of JSlider into the paintIcon(Component, Graphics, int, int)
method.  It won't take my vtcSlider (for lack of a better name)
component.  I have looked at the HorizontalSliderThumbIcon.paintIcon(...)
method and the reason it won't take my vtcSlider component is 
because there is a line that casts a Component to JSlider.
However, the code in that method does not depend on whether a 
Component is a JSlider  customer  or not.  So why is the class casting
necessary?

I am using Windows NT 4.0 with patch 3.
(Review ID: 54979) 
======================================================================
Posted Date : 2005-09-19 16:25:28.0

N/A

This seems like a reasonable request. There is nothing specific to the JSlider that justified the cast in MetalIconFactory. The methods used are hasFocus() and isEnabled() - both of which are defined in Component.
  xxxxx@xxxxx   2001-11-16
Contribution-Forum:https://jdk-collaboration.dev.java.net/servlets/ProjectForumMessageView?messageID=12162&forumID=1463
Posted Date : 2006-03-21 03:03:00.0

To remove casting component to JSlider from MetalIconFactory. Other xxxIconFactories don't contain such functionality at all.
Posted Date : 2008-04-23 17:12:42.0