code: public SingleOutputStreamOperator<T> max(String field) {
  		return aggregate(new ComparableAggregator<>(field, input.getType(), AggregationFunction.AggregationType.MAX, false, input.getExecutionConfig()));
  	}
docs: Applies an aggregation that that gives the maximum value of the pojo data
  stream at the given field expression for every window. A field expression
  is either the name of a public field or a getter method with parentheses
  of the {@link DataStream DataStreams} underlying type. A dot can be used to drill
  down into objects, as in {@code "field1.getInnerField2()" }.
  
  @param field The field expression based on which the aggregation will be applied.
  @return The transformed DataStream.