* a special map instance field to hold all such data. Map of Objects, so casting needed everywhere.
* (laziest) instance field? reserved for instance attributes. Don’t abuse.
* (laziest) static field? reserved for class attributes. Don’t contaminate.
* return a collection? A bit clumsy but recommended by many.
* best option: avoid sharing. Stick to local vars if possible.
* 2nd best: sometimes the shared variable really belongs to another class. That class/object perhaps is already shared between your methods. Essentially use that object as a courier. More work than the laziest.