Garbage Collection cannot cope?

Question

Pretty sure this is not the case but after reading articles saying nulling objects in HashMaps is expensive I need to find a way of getting my HashMaps collected.
My webapp uses Quartz and a worker thread launched by Quartz runs some code that caches up to 1.5 million key value pairs in a HashMap. Believe me this is faster than going to the database several hundred thousand times to lookup. But just before the task finishes I call clear() on the HashMap and then set it to null.
However a separate task follows that does a similar thing with a different set of key value pairs in the HashMap. The first set are not collected. And so on until by the 4th one to run I run out of the 4GB of RAM I have allocated to Tomcat, in which all this runs. So it appears to me that it never gets a chance to collect the value objects from the HashMap. I smy only option to loop through all entries in the HashMap nulling both key and value?
Thx.
David

Answer 1

1) The garbage collector can cope just fine thanks.
2) Setting things to null is dumb and pointless
3) Your design has some major flaws.
That said the real issue here is that you are leaking memory. You'll have to address that. The garbage collector will release memory held by objects that do not have any references. Your's apparently do (likely) or you have previously configured the garbage collector in some way to make it incompatible with your needs (unlikely)
You will probably not like anything I have had to say but I would encourage you to know that setting anything to null isn't a solution for anything.