code: public static Class<?> boxType( Class<?> primitiveType )
      {
          Class<?> c = wrapperMap.get( primitiveType );
          if ( c != null )
              return c;
          throw new InterpreterError(
              "Not a primitive type: "+ primitiveType );
      }
docs: Get the corresponding java.lang wrapper class for the primitive TYPE
  class.
  e.g.  Integer.TYPE -> Integer.class