What is the openjdk formula, actually?

[bartekpacia]

Output of brew config

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Output of brew doctor

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Description of issue

Hi, first of all - thank you to everyone maintaining and contributing to Homebrew. I love it.

Now, onto my question: I'm not sure what is the openjdk formula. Is this a distribution of Java by Homebrew? Is it just a upstream build?

I know that there are distributins of JDKs (e.g. Temurin by Eclipse, Amazon Coretto, even Microsoft have one). E.g. the official setup-java GitHub action allows for specifying many distributions, but openjdk is not one of them:

Another, but related question: why is openjdk a formula, but e.g. temurin is a cask?

I'm sorry if my question doesn't necessarily makes sense; in that case I'd be grateful for pointing out flaws in my understanding. Thank you.

[SMillerDev]

Now, onto my question: I'm not sure what is the openjdk formula. Is this a distribution of Java by Homebrew? Is it just a upstream build?

Every formula is a build of the software upstream provides, compiled on Homebrew CI. In the OpenJDK case: https://openjdk.org/ is upstream. And everything in the list you posted are builds of it by different vendors.

Another, but related question: why is openjdk a formula, but e.g. temurin is a cask?

Because a formula is an upstream project that can (and will) be compiled by brew. And a cask is a Homebrew distribution of precompiled binaries, like the temurin project or Firefox provides.

[bartekpacia]

I see, this confirms my suspicions. Thank you.