Does assigning objects to null in Java impact garbage collection?
Not necessarily. An object becomes eligible for garbage collection when there are no live threads anymore that hold a reference to the object.
Purpose of Nulling and Assisting the Garbage Collector
Explicit nulling refers to the practice of intentionally assigning the value null to reference objects when they are no longer needed. The purpose of nulling is to assist the garbage collector in reclaiming memory by making objects unreachable earlier. In modern Java garbage collection, the process is optimized, and objects are typically cleaned up shortly after they become unreachable. This occurs when local variables go out of scope upon method completion or when a class instance is no longer referenced for fields.
Local Variables and Nulling
However, explicitly setting a reference to null instead of letting the variable go out of scope does not significantly assist the garbage collector unless the object held is exceptionally large. Local variables naturally go out of scope when the method returns, and setting them to null is redundant since the variables cease to exist anyway. If there are no other references to the objects that the variables pointed to, those objects become eligible for garbage collection.
Reachability of Objects and Nulling
The key factor in determining an object's reachability is whether it can participate in ongoing computations. If your code refers to a local variable, and there are no other references to it, assigning null to it might cause the object to be collected. However, this could result in a null pointer exception or alter the program's behavior. If neither of these consequences occurs, it suggests that the variable was unnecessary in the first place. Techniques such as explicit nulling or object pooling, which were once considered beneficial for performance optimization, are now obsolete and may even have negative effects. The advancements in memory allocation and garbage collection have significantly reduced their necessity and potential benefits.