[hibernate-dev] Re: Regarding lazy initialization of ArrayList

Hey Nathan,

I like the idea in general and but you have to be careful with changing 
this as I assume this was done to save memory by creating the list, only 
when at least one element would be added to the list. I guess if we 
always initialize the list, we'd have to do something like the following 
in the end `this.activeFactoryNames = activeFactoryNames.isEmpty() ? 
Collections.emptyList() : activeFactoryNames` which is probably not that 
bad, assuming we probably already do something similar.

I don't think anyone would object to such an improvement regarding NPE 
safety as long as the final memory consumption stays the same. It would 
be a pity though if we unnecessarily created lots of empty ArrayLists.

Am 18.08.2020 um 22:18 schrieb Nathan Xu:
> This is my first message posted here after I finally succeeded in 
> subscribing to Hibernate dev mail list.
>
> As well known, we utilized the following 'lazy initialization' pattern 
> extensively in our codebase to save memory:
>
> if ( activeFactoryNames == null ) {
>      activeFactoryNames = new ArrayList<>();
> }
> However, even since JDK7, ArrayList has gone through refactoring to 
> keep from allocating
> memory for 10 elements in advance, if the instance was created by 
> default constructor and the allocation of memory
> is only done when some element is really added in future. Namely, 
> ArrayList has the lazy initialization feature built-in.
> E.g., see 
> https://stackoverflow.com/questions/33688753/jdk-api-documentation-is-incorrect-for-arraylist-constructor-is-that-a-bug 
>
> for details. You can also browse the source code of ArrayList to confirm.
> Screen Shot 2020-08-18 at 4.06.58 PM.png
> Needless to say, the lazy initialization pattern has serious NPE issue 
> if it is not coded carefully (which is tedious and error-prone per se).
> As an active Hibernate v6 contributor, I am troubled by such NPE issue 
> again and again.
> Is it a good timing to get rid of the above lazy initialization 
> pattern for now?
> Hopefully my message is good food for thought. No finger pointing. 
> Just curious.
>
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