What is GC Root First of all, we know the marking algorithm, the JVM’s marking algorithm can be understood as a reachability algorithm, so all reachability algorithms will have a starting point, and this starting point is the GC Root. That is, it is necessary to find all living objects through the GC Root, and then all the remaining unmarked objects are the objects to be recycled. Characteristics of GC Root Objects that are alive at the current moment!