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Conclusion. If you're just getting your feet wet with Java then installing either Java SE 8 or Java SE 11 is your best bet. While other editions like EE add extra functionality, the SE has all of the essential libraries you need.
The biggest difference between OpenJDK and Oracle JDK is licensing. OpenJDK is completely open source Java with a GNU General Public License. Oracle JDK requires a commercial license under Oracle Binary Code License Agreement. But there are many other differences within support and cost, too.
The move from AdoptOpenJDK to Eclipse Adoptium is now complete. The same great community that brought you high quality Java binaries for the last four years at AdoptOpenJDK is now fully productive at Adoptium.
LTS builds produced by AdoptOpenJDK are: High-quality, reliable, and secure.
In short:
Explanation:
Prebuilt OpenJDK (or distribution) — binaries, built from http://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 http://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.
---------------------------------------------------------------------------------------- | Provider | Free Builds | Free Binary | Extended | Commercial | Permissive | | | from Source | Distributions | Updates | Support | License | |--------------------------------------------------------------------------------------| | AdoptOpenJDK | Yes | Yes | Yes | No | Yes | | Amazon – Corretto | Yes | Yes | Yes | No | Yes | | Azul Zulu | No | Yes | Yes | Yes | Yes | | BellSoft Liberica | No | Yes | Yes | Yes | Yes | | IBM | No | No | Yes | Yes | Yes | | jClarity | No | No | Yes | Yes | Yes | | OpenJDK | Yes | Yes | Yes | No | Yes | | Oracle JDK | No | Yes | No** | Yes | No | | Oracle OpenJDK | Yes | Yes | No | No | Yes | | ojdkbuild | Yes | Yes | No | No | Yes | | RedHat | Yes | Yes | Yes | Yes | Yes | | SapMachine | Yes | Yes | Yes | Yes | Yes | ----------------------------------------------------------------------------------------
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
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)
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.
Difference between OpenJDK and AdoptOpenJDK
The first provides source-code, the other provides builds of that source-code.
Adoptium of the Eclipse Foundation, formerly known as AdoptOpenJDK, is only one of several vendors distributing implementations of the Java platform. These include:
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
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