Isn't AdoptOpenJDK using (the JVM of) OpenJDK?

Question

The AdoptOpenJDK project seems to ship JDKs bundled with HotSpot JVM (as one possible option). But what is its relationship with OpenJDK then?

I understand the word OpenJDK can be ambiguous. Here I am referring to (quoted from Wikipedia)

a free and open-source implementation of the Java Platform, Standard Edition (Java SE).

which I think already contains a JVM.

"_AdoptOpenJDK uses infrastructure, build and test scripts to produce prebuilt binaries from OpenJDK™ class libraries and a choice of either the OpenJDK HotSpot or Eclipse OpenJ9 VM_" – https://adoptopenjdk.net/ — Slaw, Oct 28 '19 at 10:07
I'm voting to close this question as off-topic because it is not a question about programming, but rather, a question about third-party projects and their relationship to each other. — RealSkeptic, Oct 28 '19 at 10:10
Well, different JVM implementations still need to follow the spec so you can choose any that fits your needs. The difference often lies in implementation details like how the JIT compiler or garbage collectors operate or different runtime options. Any JVM that passes the TCK verification should be able to run any Java program so you're free to choose what fits your needs or platform best - and AdoptOpenJDK just provides that choice. — Thomas, Oct 28 '19 at 10:16
@Slaw That all makes sense now. I thought HotSpot refers to the Oracle HotSpot JVM exclusively. I would be happy to mark this post as accepted if you can summarize your comment in an answer. Besides, would you mind elaborate on which part of OpenJDK code is used (I guess primarily javac and rt.jar?) when the OpenJ9 JVM is chosen? — wlnirvana, Oct 28 '19 at 12:07
@RealSkeptic what about the linked question in the post? Also the sample question "Do Swift-based applications work on OS X 10.9/iOS 7 and lower?" at https://stackoverflow.com/tour — wlnirvana, Oct 28 '19 at 12:11
I am not too happy about the linked question, but apparently, it provides value for programming because it asks for comparison between two environment, the answers to which may well be relevant for *development* of code. However, the relation of two projects is a legal question that has little to bear on programming. — RealSkeptic, Oct 28 '19 at 12:18
Related: [*Difference between JVM and HotSpot?*](https://stackoverflow.com/q/16568253/642706) and [*Differences between Oracle JDK and OpenJDK*](https://stackoverflow.com/q/22358071/642706). — Basil Bourque, Dec 12 '19 at 07:31
Also related: [*Difference between OpenJDK and AdoptOpenJDK*](https://stackoverflow.com/q/52431764/642706). — Basil Bourque, Jun 24 '20 at 06:06
Update: *AdoptOpenJDK* has changed its name to *Adoptium*, as part of its [move to the Eclipse Foundation](https://blog.adoptopenjdk.net/2020/06/adoptopenjdk-to-join-the-eclipse-foundation/). — Basil Bourque, Jun 24 '20 at 06:06

Basil Bourque · Accepted Answer · 2021-01-21T08:38:05.060

Update: AdoptOpenJDK has changed its name to Adoptium, as part of its move to the Eclipse Foundation.

OpenJDK provides complete source code for a full implementation of the Java Platform as defined in the Java Specifications, JSRs, and JEPs. An implementation of the Java platform includes many things, among them:

A Java programming language compiler to create .class Java bytecode files from your .java source code files.
A Java Virtual Machine (JVM) that can, at runtime, interpret and/or compile those Java bytecode files, turning them into executable code that can run on the host computer’s cores using the native instruction set of that CPU.
A runtime environment that connects Java apps with the host machine’s resources such as file system and network facility.
A required set of Java class libraries (java.util, java.time, etc.).

An implementation of Java has the option of providing a Just-In-Time (JIT) compiler/optimizer as part of the JVM. The OpenJDK project includes source code for the HotSpot JIT.

People providing builds or installers for the Java Platform are free to use HotSpot or to choose another JIT compiler technology. OpenJ9 in one such alternative JIT, developed at IBM, now open-sourced through the Eclipse Foundation, and provided free-of-charge. In the past, another alternative JIT was JRockit, owned by Oracle. Parts of JRockit have been merged into the current version of HotSpot.

The AdoptOpenJDK project offers you choice of either the HotSpot engine provided by Oracle via the OpenJDK project or the alternative OpenJ9 engine provided by the Eclipse Foundation.

With either choice you get the same class libraries from OpenJDK codebase, the same tools including Mission Control and Flight Recorder from OpenJDK, and the same utilities from OpenJDK. Only the JIT/JVM is different whether you choose HotSpot or OpenJ9.

AdoptOpenJDK is only one of several vendors providing distributions of Java techonology as binaries/installers. Most of these are based mostly, if not entirely, on the OpenJDK project’s source code releases. Here is a flowchart showing you the various vendors.

And here is a list of possible motivations to consider in selecting a vendor.

Thanks for the very clear answer. So AdopOpenJDK may actually adopt no only (the library) part of OpenJDK, but (the JVM) part of OpenJ9. Is that correct? — wlnirvana, Dec 13 '19 at 05:16

Isn't AdoptOpenJDK using (the JVM of) OpenJDK?

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