Non va lo stesso... ho risolto con questo orrendo metodo 
codice:
Enumeration e = null;
ZipEntry ze;
try{
JarFile jf = new JarFile("SCRAP.jar");
e = jf.entries();
}
catch(Exception rEx){} // failed to open
files=new Vector();
String base="scrap/dtdEditor/gui/components/";
while(e.hasMoreElements()){
ze = (ZipEntry)e.nextElement();
String fileName = ze.getName();
if(fileName.startsWith(base) && fileName.endsWith(".class") && !fileName.endsWith("Line.class") && !fileName.endsWith("ShapeMaker.class") )
files.add(fileName.substring(fileName.indexOf(base)+base.length()));
}