code: public static Builder builder(CoGroupFunction udf, Class<? extends Key<?>> keyClass, int keyColumn1, int keyColumn2) {
  		return new Builder(new UserCodeObjectWrapper<CoGroupFunction>(udf), keyClass, keyColumn1, keyColumn2);
  	}
docs: Creates a Builder with the provided {@link CoGroupFunction} implementation.
  
  @param udf The {@link CoGroupFunction} implementation for this CoGroup operator.
  @param keyClass The class of the key data type.
  @param keyColumn1 The position of the key in the first input's records.
  @param keyColumn2 The position of the key in the second input's records.