JScrollBar method

Question

does anyone know what JScrollBar uses to scroll a JScrollPane? I tried to make my own scroll bar but obviously used the wrong technique because Im getting a lot of weird bugs when I scroll with it that I dont get with the custom bar.

Answer 1

here is an example of my problem, sorry for the lengthy code but you can run it to see the problem.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class Test
     public static int RIGHT = 1;
     public static int LEFT = -1;
     public static void main(String[] args)
          Test t = new Test();
          JFrame frame = new JFrame("Test");
          try{UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());SwingUtilities.updateComponentTreeUI(frame);}catch(InstantiationException e){}catch(ClassNotFoundException e){}catch(IllegalAccessException e){}catch(UnsupportedLookAndFeelException e){}
          frame.addWindowListener(new WindowAdapter(){public void windowClosing(WindowEvent e){System.exit(0);}});
          ContainerExplorer ce = t.new ContainerExplorer();
          JPanel p = new JPanel();
          p.setLayout(new BoxLayout(p,BoxLayout.Y_AXIS));
          p.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          ce.add(t.new Container(frame));
          p.add(ce);
          frame.getContentPane().add(p);
          frame.pack();
          frame.setVisible(true);
     public class Container extends JPanel
          private Image image;
          public Container(JFrame f)
               super();
               setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));
               JButton b = new JButton("ty");
               add(b);
               image = makePicture("Images/Container.gif",f);
               setPreferredSize(new Dimension(image.getWidth(null),image.getHeight(null)));
               setMinimumSize(getPreferredSize());
          public void paintComponent(Graphics g)
               g.drawImage(image,0,0,null);
     public Image makePicture(String fileName,JFrame f)
          Toolkit toolkit = Toolkit.getDefaultToolkit();
          Image image = toolkit.getImage(fileName);
          MediaTracker mediaTracker = new MediaTracker(f);
          mediaTracker.addImage(image, 0);
          try
               mediaTracker.waitForID(0);
          catch (InterruptedException e){System.err.println(e);}
          return image;
     public class ContainerExplorer extends JPanel implements Runnable
          private Thread scrollThread;
          private int scroll;
          private JScrollPane scrollPane;
          private ContainerPanels containers;
          private Component selection;
          public ContainerExplorer()
               super();
               setLayout(new BoxLayout(this,BoxLayout.X_AXIS));
               setBorder(BorderFactory.createEmptyBorder(5,0,0,0));
               setBackground(Color.white);
               scrollThread = new Thread(this);
               scroll = 0;
               add(new ScrollPanel(LEFT));
               scrollPane = new JScrollPane(containers = new ContainerPanels());
               scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
               scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_NEVER);
               add(scrollPane);
               add(new ScrollPanel(RIGHT));
               scrollThread.start();
          public void add(Container c)
               JPanel p = new JPanel();
               p.setLayout(new BorderLayout());
               p.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.RAISED,Color.gray,Color.black));
               p.add(c);
               containers.add(p,BorderLayout.CENTER);
          public void run()
               int counter = 0;
               while(true)
                    if(scroll != 0)
                         scrollPane.getHorizontalScrollBar().setValue(scrollPane.getHorizontalScrollBar().getValue()+scroll);
                         if(counter > 3 && Math.abs(scroll) < 7)
                              if(scroll > 0)
                                   scroll+=1;
                              else if(scroll < 0)
                                   scroll-=1;
                              counter = 0;
                    counter++;
                    Thread.yield();
          public class ContainerPanels extends JPanel
               public ContainerPanels()
                    super();
                    setLayout(new FlowLayout(FlowLayout.LEFT,0,0));
                    setBackground(Color.black);
               public void paintComponent(Graphics g)
          public class ScrollPanel extends JLabel implements MouseListener
               private int direction;
               public ScrollPanel(int d)
                    super();
                    direction = d;
                    if(direction == Test.RIGHT)
                         setIcon(new ImageIcon("Images/Right.gif"));
                    if(direction == Test.LEFT)
                         setIcon(new ImageIcon("Images/Left.gif"));
                    addMouseListener(this);
               public void mouseEntered(MouseEvent e)
                    scroll = direction;
               public void mouseExited(MouseEvent e)
                    scroll = 0;
               public void mouseClicked(MouseEvent e){}
               public void mousePressed(MouseEvent e){}
               public void mouseReleased(MouseEvent e){}
}