The sun.net.www.protocol.jar.URLJarFileCallBack is only referenced from the sun.net.www.protocol.jar.URLJarFile, which is an internal class of a non-exported package within the java.base module.

The sun.net.www.protocol.jar.URLJarFile has a:

    public static void setCallBack(URLJarFileCallBack cb)

method which takes a URLJarFileCallBack. But this method isn't referenced from any code in the JDK.

Both this method as well as the unused sun.net.www.protocol.jar.URLJarFileCallBack interface can thus be removed.

Historically, the sun.net.www.protocol.jar.URLJarFileCallBack was implemented from within the "deploy" module which is no longer present in mainline since several releases.