Past exam of the year 1 of the computer science course of the University of Oxford / 2021 / Imperative programming / 8 / d / i / Solution

Garbage collection automatically reclaims allocated memory that is no longer reachable by the running program. Garbage collection roots such as active references and static storage lead through object-reference fields to reachable software objects in heap memory. A tracing garbage collection implementation preserves reachable software objects and can reclaim unreachable ones, including unreachable cycles.

An software object becoming unreachable is different from its state being old or its last object method call having finished. A retained reference can keep it live indefinitely. Collection timing is an implementation matter; automatic reclamation does not promise that an software object is reclaimed immediately when the final useful reference disappears.