Multitudes of Objects: First Implementation and Case Study for Java

Abstract In object-oriented programs, the relationship of an object to many objects is usually implemented using indirection through a collec-tion. This is in contrast to a relationship to one object, which is usually implemented directly. However, using collections for relationships to many objects does not only mean that accessing the related objects always re-quires accessing the collection first, it also presents a lurking maintenance problem that manifests itself when a relationship needs to be changed from to-one to to-many or vice versa. Continuing our prior work on fixing this problem, we show how we have extended the Java 7 programming language with multiplicities, that is, with expressions that evaluate to a number of objects not wrapped in a container, and report on the experience we have gathered using these multiplicities in a case study. ein Vieles, welches kein Eines ist (a multitude which is not a one) — inspired by Georg Cantor’s conception of a set as “jedes Viele, welches sich als Eines denken läßt”, i.e., any multitude which can be thought of as a one