Font.createFont creates temporary files in /var/tmp and does not clean them up. This eventually leads to filling the device. The following source shows this:

import java.awt.*;
import java.io.*;

public class FontTest
{
    public static void main(String [] args)
    {
        File file = new File("/usr/openwin/lib/X11/fonts/TrueType/Arial.ttf");
        try
        {
            FileInputStream in = new FileInputStream(file);
            Font arial = Font.createFont(Font.TRUETYPE_FONT, in);
        }catch(Exception e) { e.printStackTrace(); }
    }
}

% javac FontTest
% ls /var/tmp/*.ttf
ls: No match.
% java FontTest
% !ls
ls /var/tmp/*.ttf
/var/tmp/font9432.ttf
% java FontTest
% !ls
ls /var/tmp/*.ttf
/var/tmp/font37475.ttf /var/tmp/font9432.ttf