public  void add(Permission perm) 
{
        if (!isReadOnly()) {
            Permission prev = permissions.put(perm.getName(), perm);
            /*
             * If the permission already existed but with only "read" or "write"
             * set, then replace with both set.
             */
            if (prev != null && !prev.getActions().equals(perm.getActions())) {
                Permission np = new PropertyPermission(perm.getName(),
                        "read,write"); //$NON-NLS-1$
                permissions.put(perm.getName(), np);
            }
        } else {
            throw new IllegalStateException();
        }
}

 public Enumeration<Permission> elements() 
{
        return permissions.elements();
}

 public boolean implies(Permission perm) 
{
        Enumeration< Permission > elemEnum = elements();
        while (elemEnum.hasMoreElements()) {
            if ((elemEnum.nextElement()).implies(perm)) {
                return true;
            }
        }
        /*
         * At this point, the only way it can succeed is if both read and write
         * are set, and these are separately granted by two different
         * permissions with one representing a parent directory.
         */
        return perm.getActions().equals("read,write") //$NON-NLS-1$
                && implies(new PropertyPermission(perm.getName(), "read")) //$NON-NLS-1$
                && implies(new PropertyPermission(perm.getName(), "write")); //$NON-NLS-1$
}