Peculiar effect when scrolling JScrollPane

Question

How can I deal with this weird effect when scrolling using the JScrollArea:

The code:

import java.util.*;
import java.util.prefs.BackingStoreException;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.swing.*;

import javax.imageio.*;

public class Main extends JFrame implements ActionListener, AdjustmentListener{
    CustomComponent cc;
    JScrollPane jsp;

    public static void main(String[] args) {
        Main m = new Main();
    }

    public Main(){
        setTitle( "Diverse Testari 7");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(600, 400);

        cc = new CustomComponent();
        cc.setImage("rgbcmy.jpg");

        jsp = new JScrollPane( cc,
                JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED );
        jsp.setPreferredSize( new Dimension( getWidth(), getHeight() ) );
        jsp.setOpaque( true );
        jsp.setBackground( Color.DARK_GRAY );
        jsp.getVerticalScrollBar().addAdjustmentListener(this);
        jsp.getHorizontalScrollBar().addAdjustmentListener(this);
        setBackground( Color.red );

        add( jsp );
        setVisible( true );
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("EVENT: " + e.toString() );

    }

    @Override
    public void adjustmentValueChanged(AdjustmentEvent arg0) {
        // TODO Auto-generated method stub

    }

}

class CustomComponent extends JPanel{
    BufferedImage img = null;
    public void setImage( String str ){
        try {
            img = ImageIO.read( new File( str ) );
            System.out.println(img.getColorModel().toString());
            System.out.println("SUCCESS!");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public Dimension getPreferredSize() {
        // TODO Auto-generated method stub
        return new Dimension(img.getWidth(), img.getHeight() );
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.setClip(100, 100, 100, 100);
        System.out.println("paintComponent");

        if( img != null )
        {
            System.out.println("Obs: Imagine existenta!");
            g2d.drawImage(img, null, 0,0);
        }
        else
        {
            System.out.println("Eroare: nu este imaginea!");
        }
    }//*/
}

Answer 1

this is common issue where paint code isn't optimized, part of side effect is possible to removing by disable flickering, have to set additonal parameters for JViewports ScrollMode

JViewport viewPort = jsp.getViewport();
viewPort.setScrollMode(JViewport.BLIT_SCROLL_MODE);
viewPort.setScrollMode(JViewport.BACKINGSTORE_SCROLL_MODE);
viewPort.setScrollMode(JViewport.SIMPLE_SCROLL_MODE);

and by notifying by super.paintComponent(g); too +1 for Óscar Gómez Alcañiz

Answer 2

try to call super.paintComponent(g) right at the beginning of the paintComponent overridden method. Like this:

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    // rest of the method's code

Hope this helps! Good luck!