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