How does the garbage collection mechanism perform object cleanup in memory?

The Garbage Collector mechanism in Java automatically frees memory occupied by objects that are no longer used by the program.

The main principle is the determination of object reachability:

• Objects that are not referenced from active parts of the program (stack, static variables, etc.) are considered unreachable.
• Such objects are subject to removal since they cannot be used.

The garbage collection process typically includes the following stages:

1. Marking: identifying all reachable objects.
2. Sweeping: removing all unreachable objects.
3. Compaction (optional): compressing memory to reduce fragmentation.

Java uses different garbage collection algorithms (e.g., Mark-and-Sweep, Generational GC) that optimize performance and minimize pauses.

Example:

// Create an object
Object obj = new Object();
// Remove the reference
obj = null;
// Now the object is unreachable and can be collected by the garbage collector
System.gc(); // Request to run the garbage collector (not guaranteed to execute immediately)

Thus, the garbage collector frees memory automatically, relieving the developer from manually managing memory.