Why does this nullpointer happen

Question

I am trying to create a JLabel which uses the background screenshot, and prints some text on top of it.
I have run into a problem when I attempt to manually set the Font. I think I have narrowed the problem down to the getPreferredSize() method, and I think it is related to the font metrics class. But I cant figure out.
Here is the test code (it doesn't have much applicability, but it illustrates the problem)
If you remove the line: setupImage from the setFont() method, then everything works fine, but unfortunately, I need this to determine the size of my screen capture (like I mentioned before, this doesn't make much sense in my example, but for my application, it is required)
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
public class LabelTest extends JLabel {
     public static void main(String[] args) {
          JFrame frame = new JFrame();
          LabelTest l = new LabelTest(new Point(100,100));
          l.setFont(new Font("Tahoma", Font.BOLD, 14));
          frame.add(l);
          frame.pack();
          frame.setVisible(true);
        private BufferedImage image;
          private Point point;
          public LabelTest(Point p) {
               this.point = p;
               setupImage();
          private void setupImage() {
               try {
                    Robot r = new Robot();
                    Dimension d = getPreferredSize();
                    image = r.createScreenCapture(new Rectangle(point.x, point.y, d.width, d.height));
               catch(Exception e){
                    e.printStackTrace();
          public void setFont(Font f) {
               super.setFont(f);
               setupImage(); //if you comment this out, everything works
          public void paint(Graphics g) {
               Graphics2D g2 = (Graphics2D)g;
               g2.drawImage(image,0,0,this);
               //draw the labels
               Font f = getFont();
               if(f != null) {
                    FontMetrics fm = getFontMetrics(getFont());
                    g2.setColor(getForeground());
                    g2.drawString("Test", 15, fm.getHeight()/2 - fm.getMaxDescent());
          public Dimension getPreferredSize() {
               Font f = getFont();
               if(f != null) {
                    FontMetrics fm = getFontMetrics(getFont());
                    System.err.println(fm.getHeight());
                    int hieght = fm.getHeight();
                    int width = 0;
                    width = fm.stringWidth("test");
                    return new Dimension(width + 15, hieght + fm.getHeight()*2);
               else {
                    return new Dimension(200, 200);
          public Dimension getMinimumSize() { return new Dimension(200, 200); }
     }

Answer 1

2 Questions for you guys:
1) Camickr: In my code, I wasnt recreating the background image everytime, I was simply drawing it everytime. However, now that I think about it, it would be nice to figure out if the background has changed, in order to take a new picture of it.
2) So I mentioned earlier that I was having trouble with resizing of the label. I was able to narrow it down to a test case, however, I don't know why this occurs.
In the code below, I extend the Window class, and add the JLabel to it. However, you will be able to see that when I change the Font, the resizing doesn't affect the containing Window (You can test this by clicking on the window, you will see that the width is calculated using the original font, before the setFont call).
The wierd thing, is that if I dont subclass Window, and just use a Window instance in my main method, everything works fine. Now I could do this, but I would like to know why this resizing problem is happening.
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
public class LabelTest extends Window{
     public static void main(String[] args) {
          JFrame frame = new JFrame();
          frame.setPreferredSize(new Dimension(300,400));
          LabelTest l = new LabelTest(frame, new Point(500,500), "My long string 222333111444555");
          l.setFont(new Font("Tahoma", Font.BOLD, 14));
          frame.pack();
          frame.setVisible(true);
          l.setVisible(true);
     private BubbleLabel bubble;
     public LabelTest(JFrame owner, Point startingPoint, String text) {
          super(owner);
          setupBubble(startingPoint, text);
     public LabelTest(JDialog owner, Point startingPoint, String text) {
          super(owner);
          setupBubble(startingPoint, text);
     private void setupBubble(Point startingPoint, String text) {
          bubble = new BubbleLabel(startingPoint, text);
          this.setLocation(startingPoint);
          this.setLayout(new BorderLayout());
          this.add(bubble, BorderLayout.CENTER);
          this.pack();
     public void setFont(Font f) { bubble.setFont(f); }
     public class BubbleLabel extends JLabel {
          private String myText;
        private BufferedImage image;
          private Point point;
          public BubbleLabel(Point p, String text) {
               this.point = p;
               this.myText = text;
               setupImage();
               this.addMouseListener(exitListener);
          private void setupImage() {
               if(point ==  null) {
                    return;
               try {
                    Robot r = new Robot();
                    Dimension d = getPreferredSize();
                    image = r.createScreenCapture(new Rectangle(point.x, point.y, d.width, d.height));
               catch(Exception e){
                    e.printStackTrace();
          public void setFont(Font f) {
               super.setFont(f);
               setupImage();
          public void paint(Graphics g) {
               Graphics2D g2 = (Graphics2D)g;
               g2.drawImage(image,0,0,this);
               //draw the labels
               Font f = getFont();
               if(f != null) {
                    FontMetrics fm = getFontMetrics(getFont());
                    g2.setColor(Color.GREEN);
                    g2.drawString(myText, 15, 25 + fm.getHeight()/2 - fm.getMaxDescent());
          public Dimension getPreferredSize() {
               Font f = getFont();
               if(f != null) {
                    FontMetrics fm = getFontMetrics(getFont());
                    int hieght = fm.getHeight();
                    int width = 0;
                    width = fm.stringWidth(myText);
                    System.err.println(width + 15);
                    return new Dimension(width + 15, hieght + fm.getHeight()*2);
               else {
                    return new Dimension(200, 200);
          public Dimension getMinimumSize() { return new Dimension(200, 200); }
          private MouseListener exitListener = new MouseAdapter() {
               public void mouseClicked(MouseEvent e) {
                    System.err.println(BubbleLabel.this.getBounds());
}