Comments on: Sequences Performance Tip

By: Jonathan Giles

Jonathan Giles — Sun, 18 Jul 2010 23:06:02 +0000

Lichti,

Yes, if the sequence comprehension is bound, and then MAX is changed, the sequence comprehension is recomputed, which means that the loop is run again.

In the second code snippet, this will lead to a bunch of sequences being created and then GC’d.

In the third code snippet, this will not lead to massive memory consumption as only one new sequence is created.

Therefore, yes, it’s avoidable if you take the advice given in this post, and use the last code snippet, rather than the second one.

By: Lichti

Lichti — Sun, 18 Jul 2010 12:52:48 +0000

So what happens, when binding the sequence comprehension from above and then changing the MAX value?
I think a new sequence instance is created too, because trying this several times leads to massive memory consumption.
Is this avoidable somehow?

By: Jonathan Giles

Jonathan Giles — Fri, 09 Jul 2010 05:32:09 +0000

Yes, this is correct. In this case a sequence is more like an ArrayList in Java, rather than an array.

By: Alan Lee

Alan Lee — Fri, 09 Jul 2010 04:56:48 +0000

Another thing to watch out for.
Sequence is NOT an array.
So you should not use code for array manipulation with sequences.
This is especially true in a loop where you are deleting items from a sequence, the index might not point to the itme you have in mind after an item in the middle gets deleted.

By: PhiLho

PhiLho — Thu, 08 Jul 2010 08:33:59 +0000

Yes, I often advice to use the second form of the loop, for performance reasons, and because it is a more javafxish idiom (the first form is more javaish…).
If the loop is to insert new elements continuously in an existing sequence, it is better to do it in two times: create a sequence of new items, insert the sequence in the target one. And so on.