Difference between OpenJDK and Adoptium/AdoptOpenJDK

In short:

• OpenJDK has multiple meanings and can refer to:
• free and open source implementation of the Java Platform, Standard Edition (Java SE)
• open source repository — the Java source code aka OpenJDK project
• prebuilt OpenJDK binaries maintained by Oracle
• prebuilt OpenJDK binaries maintained by the OpenJDK community
• AdoptOpenJDK — prebuilt OpenJDK binaries maintained by community (open source licensed)

---

Explanation:

Prebuilt OpenJDK (or distribution) — binaries, built from https://hg.openjdk.java.net/, provided as an archive or installer, offered for various platforms, with a possible support contract.

OpenJDK, the source repository (also called OpenJDK project) - is a Mercurial-based open source repository, hosted at https://hg.openjdk.java.net. The Java source code. The vast majority of Java features (from the VM and the core libraries to the compiler) are based solely on this source repository. Oracle have an alternate fork of this.

OpenJDK, the distribution (see the list of providers below) - is free as in beer and kind of free as in speech, but, you do not get to call Oracle if you have problems with it. There is no support contract. Furthermore, Oracle will only release updates to any OpenJDK (the distribution) version if that release is the most recent Java release, including LTS (long-term support) releases. The day Oracle releases OpenJDK (the distribution) version 12.0, even if there's a security issue with OpenJDK (the distribution) version 11.0, Oracle will not release an update for 11.0. Maintained solely by Oracle.

Some OpenJDK projects - such as OpenJDK 8 and OpenJDK 11 - are maintained by the OpenJDK community and provide releases for some OpenJDK versions for some platforms. The community members have taken responsibility for releasing fixes for security vulnerabilities in these OpenJDK versions.

AdoptOpenJDK, the distribution is very similar to Oracle's OpenJDK distribution (in that it is free, and it is a build produced by compiling the sources from the OpenJDK source repository). AdoptOpenJDK as an entity will not be backporting patches, i.e. there won't be an AdoptOpenJDK 'fork/version' that is materially different from upstream (except for some build script patches for things like Win32 support). Meaning, if members of the community (Oracle or others, but not AdoptOpenJDK as an entity) backport security fixes to updates of OpenJDK LTS versions, then AdoptOpenJDK will provide builds for those. Maintained by OpenJDK community.

OracleJDK - is yet another distribution. Starting with JDK12 there will be no free version of OracleJDK. Oracle's JDK distribution offering is intended for commercial support. You pay for this, but then you get to rely on Oracle for support. Unlike Oracle's OpenJDK offering, OracleJDK comes with longer support for LTS versions. As a developer you can get a free license for personal/development use only of this particular JDK, but that's mostly a red herring, as 'just the binary' is basically the same as the OpenJDK binary. I guess it means you can download security-patched versions of LTS JDKs from Oracle's websites as long as you promise not to use them commercially.

Note. It may be best to call the OpenJDK builds by Oracle the "Oracle OpenJDK builds".

Donald Smith, Java product manager at Oracle writes:

Ideally, we would simply refer to all Oracle JDK builds as the "Oracle JDK", either under the GPL or the commercial license, depending on your situation. However, for historical reasons, while the small remaining differences exist, we will refer to them separately as Oracle’s OpenJDK builds and the Oracle JDK.

---

OpenJDK Providers and Comparison

_{Free Builds from Source - the distribution source code is publicly available and one can assemble its own build}

_{Free Binary Distributions - the distribution binaries are publicly available for download and usage}

_{Extended Updates - aka LTS (long-term support) - Public Updates beyond the 6-month release lifecycle}

_{Commercial Support - some providers offer extended updates and customer support to paying customers, e.g. Oracle JDK (support details)}

_{Permissive License - the distribution license is non-protective, e.g. Apache 2.0}

---

Which Java Distribution Should I Use?

In the Sun/Oracle days, it was usually Sun/Oracle producing the proprietary downstream JDK distributions based on OpenJDK sources. Recently, Oracle had decided to do their own proprietary builds only with the commercial support attached. They graciously publish the OpenJDK builds as well on their https://jdk.java.net/ site.

What is happening starting JDK 11 is the shift from single-vendor (Oracle) mindset to the mindset where you select a provider that gives you a distribution for the product, under the conditions you like: platforms they build for, frequency and promptness of releases, how support is structured, etc. If you don't trust any of existing vendors, you can even build OpenJDK yourself.

Each build of OpenJDK is usually made from the same original upstream source repository (OpenJDK “the project”). However each build is quite unique - $free or commercial, branded or unbranded, pure or bundled (e.g., BellSoft Liberica JDK offers bundled JavaFX, which was removed from Oracle builds starting JDK 11).

If no environment (e.g., Linux) and/or license requirement defines specific distribution and if you want the most standard JDK build, then probably the best option is to use OpenJDK by Oracle or AdoptOpenJDK.

---

Additional information

Time to look beyond Oracle's JDK by Stephen Colebourne

Java Is Still Free by Java Champions community (published on September 17, 2018)

Java is Still Free 2.0.0 by Java Champions community (published on March 3, 2019)

Aleksey Shipilev about JDK updates interview by Opsian (published on June 27, 2019)

Update 2021-09

• For versions 8 through 16, Oracle required a fee if their own Oracle JDK product was used in production, but not for dev, test, and training usages.
• For Java 17, the Oracle JDK product is available under a new No-Fee Terms and Conditions license, discussed on the Oracle company blog.

On my first reading, it appears this new license makes production use free-of-cost (along with dev, test, and training usages), except for products sold for a fee while bundling the Oracle JDK product. But I am not an attorney, so read the terms yourself and consult legal advice as needed.

Keep in mind that many other vendors continue to provide implementations of the Java specs, as shown in the flowchart below. Some of these vendors sell support plans, either optionally or as a requirement for use of their product. Never assume, always read the detailed requirements for any distribution you obtain.

Another 2021 update: Add Microsoft to the list of vendors seen below.

---

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

---

OpenJDK ➙ source code
Adoptium/AdoptOpenJDK ➙ builds

Difference between OpenJDK and AdoptOpenJDK

The first provides source-code, the other provides builds of that source-code.

• OpenJDK is an open-source project providing source-code (not builds) of an implementation of the Java platform as defined by:
  • the Java Specifications
  • Java Specification Request (JSR) documents published by Oracle via the Java Community Process
  • JDK Enhancement Proposal (JEP) documents published by Oracle via the OpenJDK project
• AdoptOpenJDK is an organization founded by some prominent members of the Java community aimed at providing binary builds and installers at no cost for users of Java technology.

Several vendors of Java & OpenJDK

Adoptium of the Eclipse Foundation, formerly known as AdoptOpenJDK, is only one of several vendors distributing implementations of the Java platform. These include:

• Eclipse Foundation (Adoptium/AdoptOpenJDK)
• Azul Systems
• Oracle
• Red Hat / IBM
• BellSoft
• SAP
• Amazon AWS
• … and more

See this flowchart of mine to help guide you in picking a vendor for an implementation of the Java platform. Click/tap to zoom.

Another resource: This comparison matrix by Azul Systems is useful, and seems true and fair to my mind.

Here is a list of considerations and motivations to consider in choosing a vendor and implementation.

Some vendors offer you a choice of JIT technologies.

To understand more about this Java ecosystem, read Java Is Still Free