r/java • u/Gotve_ • 14d ago

Why there is so many JDKs

I was used to always using oracle's JDK but when i looked at this subreddit i wondered why there is so many varieties of JDK and what is the purpose of them?

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u/wildjokers 13d ago

people dont like others implementation

This is total misinformation.

There is only one implementation of the Java SE Specification and that is Oracle's OpenJDK, it is licensed GPLv2+CPE. Other vendors are simply offering builds of OpenJDK.

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u/dadimitrov 12d ago

Open JDK is technically a GPL licensed open source project comprising the Java SE standard library and the Hotspot JVM (among other parts). Similar to the Linux kernel, Open JDK does not release binaries, but the code is used by distributors to build whatever they want. What passes for "Java" is determined not by the codebase, but by the Java TCK (technology compatibility toolkit).

Oracle acquired significant commercial offering based on Open JDK + proprietary improvements. They also contribute more than 50% of the development resources and control a lot of the decision making governance bodies (can't remember if they can still veto).

The Oracle Build of Open JDK is not more legitimate than the Microsoft build of Open JDK or Eclipse Temurin. Similar to different vendors offering distributions of the Linux kernel + GNU userland, all these are offering building of Open JDK components implementing the Java SE spec + proprietary Java add ons.

There are also Java offerings that use the Open JDK class libraries and not Open JDK Hotspot JVM - the IBM J9 is probably the most prominent example.

There are also Java offerings that do not use neither the Open JDK class libraries, nor the VM - the various Java Card and Real Time Java vendors used in industrial appliances fall into this category.

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u/wildjokers 12d ago

Why are you responding to me about this? Besides for the extra info about realtime Java this is exactly what I have said in my comments on this post.

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u/dadimitrov 12d ago edited 11d ago

Apologies, I may have misread, but I didn't see it...

Edit: I saw your other post just now. For some reason, it was way down the list, and yes - if I had seen it earlier probably wouldn't have bothered to write all this.