When are Java objects eligible for garbage collection?

objects become eligible for garbage collection when they are no longer reachable or referenced by any active part of the program. The Java Virtual Machine (JVM) automatically handles garbage collection, freeing up memory by deallocating objects that are no longer needed.

The exact moment when an object becomes eligible for garbage collection is determined by the JVM's garbage collection algorithm, which includes various strategies like mark-and-sweep, generational collection, or concurrent collection. However, the general principle for determining eligibility is based on the reachability of objects through references.

An object is considered eligible for garbage collection if it cannot be reached through any live references in the program. In other words, if there are no references pointing to an object or if all references to the object have been set to null, the object becomes eligible for garbage collection.

Here are a few scenarios where objects may become eligible for garbage collection:

1. Out of Scope: When an object goes out of scope, meaning it is no longer accessible within the current block, method, or scope of execution, it becomes eligible for garbage collection.
2. Assignment to null: If all references to an object are explicitly set to null, indicating that they no longer point to the object, it becomes eligible for garbage collection.
3. Reassignment: When a reference variable is reassigned to another object, any previously referenced object becomes eligible for garbage collection if no other references exist.
4. Circular References: If a group of objects references each other in a circular manner, but none of them are reachable by any live reference from outside the group, the entire group becomes eligible for garbage collection.

The decision of when to perform garbage collection and actually reclaim memory is managed by the JVM. The JVM analyzes the memory usage, heap space availability, and other factors to determine the optimal time for garbage collection.