Flowcharts represent flow of control, not flow of information. Flowcharting formally captures steps and the linkages between them that describe the transfer of the flow of control that are often based on decisions: in particular, conditional branches and loops.
Flow of control is about what is done or happens next, and (sadly) not about the required data to perform that step.
According to Wikipedia, there are some extensions for the flow of data; however, they are basically limited to documents and files.
Generally speaking, state is poorly represented in flowcharting; there is virtually no notion of data, variables, scopes, lifetimes, or types. So, data (and metadata about that data, such as allowed or expected types) is mostly documented informally with human language description in the text within individual steps of the flowchart.
Input & Output in flowcharting is meant to indicate communication with another independent and top-level process (even if it is just a later running copy of one's self). As such this communication is about reading/writing to disc or to a network.
A getter does not qualify as input or output, which is to say communication with another independent process, so I think that is out. I don't think they even had getter's when flowcharting was first applied to software design (circa 1950).
You might look in to UML.