What methods are used for garbage collection in systems with automatic memory management?

In systems with automatic memory management through garbage collection (GC), the following methods are usually used:

• Mark-and-Sweep: the system first marks all objects reachable from root references, then deletes all unmarked objects.
• Copying: memory is divided into two regions, active objects are copied from one region to another, freeing the old region.
• Reference Counting: each object maintains a reference count, and when it reaches zero, the object is deleted.
• Generational Garbage Collection: objects are divided into generations (young and old), as most objects quickly become unnecessary, collection is often performed in the young generations for optimization.

In Java, for example, a combination of these methods with different algorithms for different generations is used, which allows efficient memory management.