code: public void add(ObjectType type, boolean explicit) {
          int index = factory.getIndexOfType(type);
          if (!exceptionSet.get(index)) {
              ++size;
          }
          exceptionSet.set(index);
          if (explicit) {
              explicitSet.set(index);
          }
  
          commonSupertype = null;
      }
docs: Add an exception.
  
  @param type
  the exception type
  @param explicit
  true if the exception is explicitly declared or thrown, false
  if implicit