Why you should never use synchronized on Optional java object

Question

I m learning about java optional wrapper, to do so I m reading the following tutorial

however I have a simple question that is not answered in the article: in item 25: Avoid Using Identity-Sensitive Operations on Optionals they are mentioning to NEVER use an optional object in a synchronized way like this:

Optional<Product> product = Optional.of(new Product());

synchronized(product) {

    ...

}

but there is no explanation why, so please would any one here explain to me why this is a bad practice ???

https://docs.oracle.com/javase/8/docs/api/java/lang/doc-files/ValueBased.html — Amadan, Jul 10 '19 at 11:39
Thanks @Amadan :) now I will read about value-based classes to know more :) — Mohammed Housseyn Taleb, Jul 10 '19 at 11:42
the real answer is [here](https://stackoverflow.com/a/47545351/1059372) — Eugene, Jul 10 '19 at 11:43
@Eugene I also found [this](https://rules.sonarsource.com/java/tag/java8/RSPEC-3436) — Mohammed Housseyn Taleb, Jul 10 '19 at 11:49

score 5 · Accepted Answer · answered Jul 10 '19 at 11:40

5

Because

[value-based classes] are freely substitutable when equal, meaning that interchanging any two instances x and y that are equal according to equals() in any computation or method invocation should produce no visible change in behavior"

Source (Oracle)

You can not freely substitute X and Y if there is an intrinsic lock on one of them, since doing so may produce a change in behaviour.

answered Jul 10 '19 at 11:40

Michael

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thank you so much for this answer, I found [this article](https://rules.sonarsource.com/java/tag/java8/RSPEC-3436) this also explain the same thing with an example for all who are new to java 8 like me – Mohammed Housseyn Taleb Jul 10 '19 at 11:51

Why you should never use synchronized on Optional java object

1 Answers1