When exactly does the garbage collector trigger the memory release process in the heap?

The process of freeing memory in the heap when using a garbage collector in Java is triggered when the virtual machine determines that objects in the heap are no longer reachable from root references (such as from the stack or static variables). This occurs automatically and can be triggered in the following cases:

• When available memory in the heap runs out or falls below a certain threshold.
• When explicitly calling System.gc(), although this is only a recommendation to the JVM.

The garbage collector scans objects, marking reachable ones, and then frees the memory occupied by unreachable objects. The exact timing of the garbage collector's run depends on the JVM implementation and its settings.