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javaclassarraylistgarbage-collection
bill
bill

Reputation: 51

Garbage Collection on an unnamed class

How does the Java GC work on a simple situation like this:

ArrayList<Object> list = new ArrayList<>();

list.add(new Object());
list.add(new Object());
//do something with objects
list.remove(0);

Upvotes: 1

Views: 50

Answers (2)

Tobias
Tobias

Reputation: 4074

First off: the class Object is not an "unnamed class". If at all, one would use this term in the context of anonymous classes.

GC retains all objects that are alive, i.e. reachable from GC roots. All other objects are discarded. Local variables are (among others) GC roots.

What you are describing is a situation where there is no reference variable pointing directly to your object, like for instance Object myObj = new Object();.

However, there is a list containing a reference to your object.

Now, what would happen if the GC were to run?

  • Before list.remove(0); your object would be marked as alive since it is indirectly reachable through the list.

  • After list.remove(0); (and assuming "do something with objects" doesn't involve establishing another reference to your object) your object wouldn't be marked as alive by the GC since it is not reachable anymore. The memory that was occupied by your object would afterwards be marked as free.

Upvotes: 1

Som Bhattacharyya
Som Bhattacharyya

Reputation: 4112

Well typically if use use the object in the "do something with objects" that causes them to be retained then they will not be garbage collected despite the list.remove call.

Also try and make sure you declare the list in the shortest scope possible. That is closest to where it is being used. That would make the list automatically fall out of scope and be GC'd earlier.

Also sometimes you may want to set the object to null after you are done using it. That as well works to get it off scope and eligible for GC.

Upvotes: 1

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