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.

Answer 1

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.