CODEWITHSUNDEEP
garbage-collection
Barry
Barry

Reputation: 1665

How does GC work when HashMap.remove(Key)

I have a Map

Map<OuterKey,Map<InnerKey,Object>> sampleMap

on this I do sampleMap.remove(OuterKey)

Now what does this imply to the inner map? would it be garbage collected on the next cycle?

Do you guys recommend me doing 

Map<InnerKey,Object> innerMap = sampleMap.remove(OuterKey);
innerMap.clear();

Does this help from the perspective of GC?

Thanks

Upvotes: 0

Views: 155

Answers (2)

ChiefTwoPencils
ChiefTwoPencils

Reputation: 13930

When there are no more references to the object it will be marked for garbage collection and it's then the gc's responsibility. It doesn't guarantee to automatically run. So clearing it wouldn't achieve anything.

That is for two reasons.

  1. Calling clear leaves you with an empty map. An empty map isn't the same thing as a map with no references to it.
  2. When you call remove you actually create another reference (innerMap) to it. If anything that hinders gc until you get rid of that one too.

Upvotes: 1

T McKeown
T McKeown

Reputation: 12857

GC only cares about references to your object, and no GC is not helped by clearing the inner map.

In your example sampleMap had the only reference to the innerMap, so when you removed the entry from sampleMap there would be no other refs to your innerMap (after your local variable innerMap goes out of scope), so you have dereferenced the innerMap.

GC would mark your innerMap as eligible for finalization, if a finalizer was coded it would be run. After that you can consider your object GC'd.

Of course when does GC run? It's not something you can predict outside of brute force calling it (via GC.Collect()) and that should only be done in rare/unique circumstances.

Upvotes: 1

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