Keskustelu: Ohjelmointikysymykset: Java: skrollaus alas hävittää kuvan JPanelista

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;

public class MainWindow extends JFrame implements ActionListener{

    private String kuva_yksi_path = ".\\kuva1.png";
    private String kuva_kaksi_path = ".\\kuva2.png";
    ImagePanel drawingPanel = null;

    //The constructor for the class MainWindow.
    public MainWindow()
	{
	makeFrame(kuva_yksi_path);
	}

   //Make frame
   public void makeFrame(String kuvaPath)
   	{
        drawingPanel = new ImagePanel(kuvaPath);

	JScrollPane scroller = new JScrollPane(drawingPanel);
        scroller.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(900,670));

        //change button
        JButton change_button = new JButton("change");
        this.getContentPane().add(change_button, BorderLayout.WEST);
		change_button.addActionListener(this);

       //scroller is the JScrollPane
        this.getContentPane().add(scroller, BorderLayout.CENTER);
        this.setVisible(true);
        this.pack();
        }

   //change the picture
   public void actionPerformed(ActionEvent e)
   	{
   	if(e.getActionCommand().equals("change"))
		makeFrame(kuva_kaksi_path);
	}

//The panel on which the drawings are done
private class ImagePanel extends JPanel
       {
       Image image = null;

       public ImagePanel(String kuva_path)
        {
				image = getToolkit().getImage(kuva_path);//load image
 				}

        //This is the method that actually paints all the drawings whenever a.
        //The shapes theselves can be defined somewhere else, but that paint method must be invoked from here.
        public void paintComponent(Graphics g)
        	{
            super.paintComponent(g); //paint background
        	Graphics2D g2 = (Graphics2D) g;

       		if (image != null)
				{ //there is a picture: draw it
				 g.drawImage(image,0, 0, 53, 77, this);
				}  //end if
 			g.drawString("text", 750, 750);//To test the scrollpane.
 			}

		public Dimension getPreferredSize()
			{
			return new Dimension(750,750);
			}
	}
    public static void main(String[] args)
    	{
        new MainWindow();
    	}
}