ImageIO.write converting to gif

Question

It seems that I can't ImageIO to convert a BufferedImage to the GIF format. Other formats work. According to the program's output (see below), ImageIO should be able to handle GIF. Yet the returned byte array is zero length. What is the problem?
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import java.io.*;
public class JPGTest {
     public static void main(String[] args) {
          try {
               Rectangle screenRectangle = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
               Robot robo = new Robot();
               // take a screenshot
               BufferedImage bufferedImage = robo.createScreenCapture(screenRectangle);
               ByteArrayOutputStream baos = new ByteArrayOutputStream();
               // this line seems to fail
               ImageIO.write(bufferedImage, "gif", baos);
               System.out.println("check whether the \"gif\" format is supported");
               String formatNames[] = ImageIO.getReaderFormatNames();
               for (int i = 0; i < formatNames.length; i ++)
                    System.out.println(formatNames);
               // returns a zero byte array when "gif" is passed into ImageIO.write above
               // yet works when "jpg" is passed in
               byte imageBytes[] = baos.toByteArray();
               System.out.println("Image bytes length: " + imageBytes.length);
          } catch (Exception e) {
               System.out.println(e.getMessage());
And here is the output:
1: the supported images, followed by
2: the obvious conversion-to-gif failure:
check whether the "gif" format is supported
BMP
bmp
jpeg
wbmp
gif
png
JPG
jpg
WBMP
JPEG
Image bytes length: 0

Answer 1

It used to be that some corporation had a patent (or something like that) on the GIF format, so you had to buy a licence from them to be able to produce GIFs. I suspect that is why Sun did not distribute software that could produce GIFs. That's my guess, anyway. Here's a link to a small bit of information about that:
http://mindprod.com/jgloss/gif.html