How is automatic garbage collection implemented in programming languages?

Automatic Garbage Collection (GC) is a memory management mechanism that automatically frees memory occupied by objects that are no longer used by the program.

Main approaches to implementing GC:

1. Reference Counting — each object has a reference count. When the count reaches zero, the object is deleted. The drawback is that it does not work with cyclic references.

2. Mark-and-Sweep — GC first marks all accessible objects, then cleans up all unmarked objects, considering them as garbage.

3. Copying Collector — memory is divided into two regions, active objects are copied from one region to another, freeing the old region.

4. Generational GC — objects are divided into generations based on their lifetime; the young generation is cleaned more frequently, increasing efficiency.

In Android, for example, Dalvik/ART uses generational GC, which runs in the background, minimizing delays and preventing memory leaks.