JScrollPane is smearing JPanel

Question

When painting to a panel inside a JScrollPane, I am having problems with the panel smearing as I scroll. It looks just as though it's repainting over what was already painted on the panel. Just as some testing, I called repaint within my paint method just to try and determine where the issue was coming from. While this didn't fix the issue nor kill my processor, it did seem to make it a little better. Could this be a problem as to the way I am drawing to the panel, or an issue with my use of the JScrollPane?
Here is my SongDisplay class that extends a JPanel:
package gui;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.swing.JPanel;
* @author tlee
public class SongDisplay extends JPanel implements /*MouseListener,*/ SongDisplayInterface
    List<SongFileWordDisplay> words = Collections.synchronizedList(new ArrayList<SongFileWordDisplay>());
    public SongDisplay()
        super();
        /*this.setPreferredSize(new Dimension(width, GuiConstants.SONG_DISPLAY_HEIGHT));
          this.addMouseListener(this);*/
    @Override
    public void paint(Graphics g)
        g.setColor(Color.BLACK);
        synchronized (words)
            for (SongFileWordDisplay word : words)
                g.drawString(word.getLyric(), word.getPoint().x, word.getPoint().y);
    public void setWidth(int width)
        this.setPreferredSize(new Dimension(width, GuiConstants.SONG_DISPLAY_HEIGHT));
        super.revalidate();
    public synchronized void addSongFileWordDisplay(SongFileWordDisplay sfwd)
        words.add(sfwd);
        this.repaint();
}

Answer 1

tristanlee85 wrote:
When painting to a panel inside a JScrollPane, I am having problems with the panel smearing as I scroll. It looks just as though it's repainting over what was already painted on the panel. Just as some testing, I called repaint within my paint method just to try and determine where the issue was coming from. While this didn't fix the issue nor kill my processor, it did seem to make it a little better. Could this be a problem as to the way I am drawing to the panel, or an issue with my use of the JScrollPane?
Here is my SongDisplay class that extends a JPanel:
package gui;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.swing.JPanel;
* @author tlee
public class SongDisplay extends JPanel implements /*MouseListener,*/ SongDisplayInterface
List<SongFileWordDisplay> words = Collections.synchronizedList(new ArrayList<SongFileWordDisplay>());
public SongDisplay()
super();
/*this.setPreferredSize(new Dimension(width, GuiConstants.SONG_DISPLAY_HEIGHT));
this.addMouseListener(this);*/
@Override
public void paint(Graphics g)
g.setColor(Color.BLACK);
synchronized (words)
for (SongFileWordDisplay word : words)
g.drawString(word.getLyric(), word.getPoint().x, word.getPoint().y);
public void setWidth(int width)
this.setPreferredSize(new Dimension(width, GuiConstants.SONG_DISPLAY_HEIGHT));
super.revalidate();
public synchronized void addSongFileWordDisplay(SongFileWordDisplay sfwd)
words.add(sfwd);
this.repaint();
It is definetly a problem in your paint--you need to call super.paint(g) as the first thing so your object will be painted correctly before you try to put your twist of the world in there.