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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.

A tracing garbage collection implementation starts from garbage collection roots and follows software object references. Software objects outside that reachable set can be reclaimed, including cycles that have no path from a root. A decorator or adapter holding a component reference keeps that component reachable while the wrapper remains reachable. The number of allocated software objects alone does not establish how much storage can be reclaimed.