code: public String makeJavaIdentifier(String id)
      {
          String jid = makeJavaId(id);
          String old = map.put(jid, id);
          if (old != null && !old.equals(id))
          {
              throw new IllegalArgumentException("both "+id+" and "+old+" makes the same java id "+jid);
          }
          return jid;
      }
docs: Returns a String capable for java identifier. Throws IllegalArgumentException
  if same id was already created.
  
  <p>Same id returns always the same java id.
  @param id
  @return