How does the garbage collector mechanism determine that an object is no longer used and can be freed?

The garbage collector mechanism in Android (based on Java) determines that an object is no longer in use based on reachability:

• An object is considered reachable if there is a reference to it from root objects (for example, from the call stack, static variables, or other reachable objects).
• If an object is unreachable, it means there are no access paths to it from active code, and it is considered garbage.

The garbage collector periodically traverses the object graph starting from the roots and marks all reachable objects. All other objects are considered unused and are freed.

Example:

Object obj = new Object(); // create an object
obj = null; // remove the reference
// now the object is unreachable and can be collected by the garbage collector

Thus, GC automatically frees memory, relieving the programmer from manually managing memory.