import java.awt.*;
import java.util.*;

import javax.swing.*;
import javax.swing.event.*;


/**
 *  Simple panel that illustrates the synchronization of two JScrollPanes.
 *  The number of elements in the two JList components do not have to be
 *  the same. The ChangeListener will synchronize their respective
 *  BoundedRangeModels and scale as necessary.
 *  <p> Note: Since it is the right JScrollBar's model-ChangeListener
 *  that listens for changes from the left JScrollBar, it is the right JList
 *  that controls the total number of elements shown in the JScrollPanes. </p>
 *
 *
 *  @author  R. Kevin Cole
 */
public class ScrollBarSynchronizer extends JPanel
{
	/**    Two JLists are created and initialized from Vectors and
	 *    then added to JScrollPanes to test the synchronized JScrollBars.
	 */
	public ScrollBarSynchronizer()
	{
		super(new BorderLayout());

		//  create something to scroll    
		Vector<String> leftData = new Vector<String>();
		Vector<String> rightData = new Vector<String>();

		for (int i = 0; i < 71; i++)
		{
			rightData.add("Right " + i);

			//  the modulo operator is used to create a different number       
			//  of elements within each scrolling region.      
			if ((i % 2) == 0)
			{
				leftData.add("Left " + i);
			}
		}

		JScrollPane leftScroller = new JScrollPane(new JList(leftData));
		leftScroller.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_NEVER);

		JScrollPane rightScroller = new JScrollPane(new JList(rightData));
		JScrollBar leftBar = leftScroller.getVerticalScrollBar();
		JScrollBar rightBar = rightScroller.getVerticalScrollBar();
		MyChangeListener listener = new MyChangeListener(leftBar.getModel());
		rightBar.getModel().addChangeListener(listener);

		JSplitPane split = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, leftScroller, rightScroller);
		add(split, BorderLayout.CENTER);
	}

	/**   Test routine.   */
	public static void main(String[] arg)
	{
		JFrame frame = new JFrame("Test ScrollBarSynchronizer");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setContentPane(new ScrollBarSynchronizer());
		frame.setSize(640, 480);
		frame.setLocation(100, 100);
		frame.setVisible(true);
	}
}

/**
 *	Synchronize the data models of any two JComponents that use a
 *	BoundedRangeModel ( such as a JScrollBar, JSlider or ProgressBar).
 *
 *	@see javax.swing.BoundedRangeModel
 *	@see javax.swing.event.ChangeListener
 *	@Author  R. Kevin Cole	
 */
class MyChangeListener implements  ChangeListener
{
	private BoundedRangeModel myModel;


	/**
	 *	@param   model  This model is forced to move in synchronization
	 *		to this ChangeListener's event-source.
	 */
	public MyChangeListener( BoundedRangeModel model )
	{
		myModel = model;
	}


//	- begin - implementation of ChangeListener
//
	/**
	 * 	Envoked when the target of the listener has changed its state.
	 */
	public void stateChanged( ChangeEvent e )
    {
		BoundedRangeModel sourceModel = (BoundedRangeModel) e.getSource();
        
		int sourceDiff  = sourceModel.getMaximum() - sourceModel.getMinimum();
		int destDiff  = myModel.getMaximum() - myModel.getMinimum();
		int destValue = sourceModel.getValue();

		if( sourceDiff != destDiff )
			destValue   = (destDiff * sourceModel.getValue())/sourceDiff;
        
		myModel.setValue( myModel.getMinimum() + destValue );
	}
//
//	- end   - implementation of ChangeListener

}