Hey everyone, I’ve just started getting into Swing and have encountered a weird problem. I’m trying to get a grid which will expand when left-clicked and retract when right-clicked. This works fine, but the positioning seems strange to me. I want the grid to start from the top-left corner, but it seems like there is some kind of invisible border there. Has anyone else seen this before? I’m sure I’m just making some newbie mistake 
public class GridScroller extends JPanel implements MouseListener{
public final static String PROG_NAME = "GridScroller";
public JPanel drawingPane;
public int clickCounter = 0;
public GridScroller(){
super(new BorderLayout());
System.out.println(PROG_NAME + ": constructor entered");
drawingPane = new DrawingPane();
drawingPane.setBackground(Color.CYAN);
drawingPane.addMouseListener(this);
JScrollPane scroller = new JScrollPane(drawingPane);
drawingPane.setLocation(0,0);
scroller.setPreferredSize(new Dimension(600, 450));
scroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
scroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
add(scroller);
}
public class DrawingPane extends JPanel{
protected void paintComponent(Graphics g){
super.paintComponent(g);
for(int i = 0; i < clickCounter; i++){
for(int j = 0; j < clickCounter; j++){
g.setColor(Color.BLACK);
g.drawRect(20, 20, i * 20 + 0, j * 20 + 0);
}
}
}
}
public void mouseReleased(MouseEvent e){
//drawingPane.setPreferredSize(new Dimension(drawingPane.getWidth() + 50, drawingPane.getHeight() + 50));
if(e.getButton() == MouseEvent.BUTTON1){
clickCounter++;
}
if(e.getButton() == MouseEvent.BUTTON3){
clickCounter--;
}
drawingPane.setPreferredSize(new Dimension((clickCounter + 2) * 20, (clickCounter + 2) * 20));
drawingPane.repaint();
drawingPane.revalidate();
System.out.println("Mouse event captured");
}
public void mouseClicked(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseExited(MouseEvent e){}
public void mousePressed(MouseEvent e){}
public static void createAndShowGUI(){
System.out.println(PROG_NAME + ": createAndShowGUI entered");
JFrame frame = new JFrame("GridScroller");
frame.setLayout(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JComponent newContentPane = new GridScroller();
newContentPane.setOpaque(true);
frame.setContentPane(newContentPane);
newContentPane.setLocation(0,0);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args){
System.out.println(PROG_NAME + ": main entered");
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run(){
createAndShowGUI();
}
});
}
}
