How Garbage Collection Works: Key Concepts Every Developer Should Know

Garbage collection is a runtime feature that automatically identifies and reclaims memory from objects that are no longer reachable by a program, reducing manual memory-management burden on developers. However, it is not instantaneous or guaranteed — for instance, calling System.gc() in Java is merely a hint to the runtime, not a command. Memory leaks can still occur when objects remain referenced but are no longer logically needed, such as items continuously added to a cache without removal. Some garbage collection phases require pausing application threads in what are called stop-the-world pauses, though modern collectors increasingly perform work concurrently to reduce latency. An object's memory is only eligible for reclamation once all references to it from GC roots are gone, making reference management a critical part of efficient memory use.