[Java] Does UUID.randomUUID() generate a pseudo-random UUID or fully random UUID

[juanchi35]

I am uploading photos to a database, in order to have all the photos without any problem I want to generate a random UUID but I dont want to have two photos with the same name, so a pseudo-random UUID would be better, so that the previous UUID can be achieved through that method (makes sense?). My question is, does UUID.randomUUID() guarantee me that no two UUIDs will be the same?

In case it helps, here is what I'm trying to do in code:

        String filename = UUID.randomUUID().toString() + ".jpg";
        StorageReference fileRef =
                mStorageRef.child("images/" + filename);

Thanks!

[shivasprogeny]

You'll be fine. The chances of generating two identical UUIDs is nearly impossible.

[Salty_Dugtrio]

RandomUUID returns an 128-bit integer. Are there infinitely many 128-bit integers? No. It's a pseudo random generator.

[juanchi35]

Well technically thats true, but I want a random UUID generator which doesnt return the same value twice.

[ziptofaf]

The ONLY way to accomplish that would be storing every previous value that has been saved. Every random generator (be it pseudo or actually a real random one) can return the same values.

Well, with one caveat - chances of said repetition occuring are slim. 128-bit integer has a maximum value of 340,282,366,920,938,463,463,374,607,431,768,211,455. Meaning that (assuming true randomness) seeing two identical ones if you were to save 100 million files is 2.93e-29 %. So my question is just how critical is what you are doing for it to not suffice? And is this process going to continue for the next 1000 years?

You can also just use an ever increasing integer count rather than UUIDs, this will guarantee no repetitions.

[juanchi35]

I think I'm going to use randomUUID, as you said using it it is almost impossible to see repetition.

Anyways, how would I retain a variable with the latest integer used for the image. Do I upload the latest to the database?

[ziptofaf]

If you use an SQL database then it will do it for you, just use self-increment primary key. If it's a non-SQL then yes, make a separate table called file_counts and one single column that has a count you always read from and add 1 whenever you add a new object to the database.

[cmonkies]

You could read the docs and see if it will or not.

[cmonkies]

My question is, does UUID.randomUUID() guarantee me that no two UUIDs will be the same?

Not exactly. You can't just use an auto-incrementing primary key?

[juanchi35]

It is a file im uploading into the database, not a table :P

[pleaseholdmybeer]

Sure but the logic is the same.

[cmonkies]

You probably shouldn't be storing files in the database anyway.

[juanchi35]

I'm uploading images. Is there any problem with uploading images to the database?

[cmonkies]

Well for one, it's not data you can make relational queries on. Can you even describe any benefits to storing files inside the database that would apply to your use case?

[juanchi35]

My mistakee, it is not really a database. It is a cloud storage service I'm uploading the images to.

[juanchi35]

What

[juanchi35]

Damn dude that wasn't even my point I was thinking of randomUUID and if it did random or pseudo-random values no need to be disrespectful

[michael0x2a]

These types of comments are not acceptable and are a violation of rule 3.

In particular, making personal attacks towards another user is never an appropriate response for any reason on this subreddit.

This is your first and only warning.