(As we all know, Java does not *write* gif's..)

I think some of the sources on Marco Schmidt's site will
do the trick in core Java, you just need to specify PNG or
JPG for the output..
<http://schmidt.devlib.org/java/image-file-code-examples.html>

HTH

Use ImageIO to read the GIF and use ImageIO to write it back out as a
PNG or JPG.

import java.awt.image.*;
import java.io.*;
import javax.imageio.*;

public class test3 {
    public static void main(String[] args) throws Exception {
        BufferedImage image = ImageIO.read(new File("button0.gif"));
        ImageIO.write(image,"PNG",new File("button0.png"));
        ImageIO.write(image,"JPG",new File("button0.jpg"));
    }
}