In Android Run Time (ART) environment, Garbage Collection could be one of the types:

Concurrent mark sweep (CMS)

A whole heap collector which frees collects all spaces other than the image space.

Concurrent partial mark sweep

A mostly whole heap collector which collects all spaces other than the image and zygote spaces.

Concurrent sticky mark sweep

A generational collector which can only free objects allocated since the last GC. This garbage collection is run more often than a full or partial mark sweep since it is faster and has lower pauses.

Mark sweep + semispace

A non-concurrent, copying GC used for heap transitions as well as homogeneous space compaction (to defragment the heap).

Acknowledgment: Android Developer Guide.