Trying to make Scrollable Functionality in Paint like program.

Question

I'm wrinting a program thats a lot like MSPaint or any of the other paint variants. I have a JPanel that all of my shapes are drawn to. I need the scroll bars to show only when the shapes, which are variants of Shape2D, are to large to be shown in the window. For some reason I just can't make heads or tails of the JScrollPane documentation. If someone can just give me an example of a class that extends JPanel and has the scroll bars on it I think that I could figure it out from there.

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
public class ScrollView extends JPanel {
    List<Line2D> lines = new ArrayList<Line2D>();
    final int DELTA = 30;
    final int PAD   =  5;
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.blue);
        for(int i = 0; i < lines.size(); i++) {
            g2.draw(lines.get(i));
    public Dimension getPreferredSize() {
        double maxX = 0, maxY = 0;
        for(int i = 0; i < lines.size(); i++) {
            Rectangle r = lines.get(i).getBounds();
            if(r.getMaxX() > maxX) maxX = r.getMaxX();
            if(r.getMaxY() > maxY) maxY = r.getMaxY();
         return new Dimension((int)(maxX+PAD), (int)(maxY+PAD));
    private JPanel getLast() {
        String[] ids = { "width", "height" };
        ActionListener al = new ActionListener() {
            Rectangle rect = new Rectangle(PAD,PAD);
            public void actionPerformed(ActionEvent e) {
                String id = e.getActionCommand();
                int w = getWidth();
                int h = getHeight();
                double x1 = 0, y1 = 0, x2 = 0, y2 = 0;
                if(id.equals("width")) {
                    double lineWidth = (w-2*PAD) + DELTA;
                    x1 = PAD;
                    x2 = x1 + lineWidth;
                    y1 = y2 = h - PAD;
                } else {
                    double lineHeight = (h-2*PAD) + DELTA;
                    x1 = x2 = w - PAD;
                    y1 = PAD;
                    y2 = y1 + lineHeight;
                lines.add(new Line2D.Double(x1, y1, x2, y2));
                repaint();
                revalidate();
                rect.setLocation((int)x2, (int)y2);
                scrollRectToVisible(rect);
        JPanel panel = new JPanel();
        for(int i = 0; i < ids.length; i++) {
            JButton button = new JButton(ids);
button.setActionCommand(ids[i]);
button.addActionListener(al);
panel.add(button);
panel.setBorder(BorderFactory.createTitledBorder("expand"));
return panel;
public static void main(String[] args) {
ScrollView test = new ScrollView();
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new JScrollPane(test));
f.add(test.getLast(), "Last");
f.setSize(400,400);
f.setLocation(200,200);
f.setVisible(true);