What is the difference between Objective-C automatic reference counting and garbage collection?

Question

With the new automatic reference counting (ARC) introduced in Xcode 4.2, we no longer need to manually manage retain / release in Objective-C.

This seems similar to

Answer 1

the short and sweet answer is as follow:

GC of java is Runtime, while ARC is compile time.

GC has reference to the objects at runtime and check for the dependencies of object runtime. While ARC appends the release, retain, autorelease calls at compiletime.