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Java / Java SE / JDK / JRE - which is which and what do I want?
Whether Java SE is the same as JDK? - Stack Overflow
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Okay, context. I'm trying out some programming languages to perhaps get into (after previously primarily doing stuff with C#). One of these is Java. I had a 2019 version of Eclipse installed from last time I wanted to learn Java. Updated it to 2021, and it tells me I need Java 11 or higher.
So I google "download Java". Oracle offers me to download Java 8 Update 291, released April 2021. I check my instaleld version. Sure enough, I have Java 8 Update 291. If I am up to date, why is Eclipse complaining, I wonder? So I google Java 11. Huh, what's that, there are versions of Java up to 16? One article mentions that Java 8 has been deprecated for years. Odd, I think, didn't Oracle tell me just now that Java 8 was released in 2021? Oh, I see, they are talking about something called "Java SE". So I google what that is. "java vs java se", I google, but all I get are articles about how Java SE is different from something called Java EE. Never heard of it, I don't want it. In the meantime, I have also googled for JDK, since I assume that I need the Java SDK to get the compilers. Maybe the JDK has a different version number than the JRE, I theoretise. But then what is this Java SE? At one point, it says it's the standard edition, but on the next page, it says it's "for reference purposes only". Whatever that means. Can I use it to run and compile Java or not, I ask.
tldr: why is there a Java 16 if Oracle tells me 8 is the latest, which one do I want to run and program with the latest Eclipse?
P.S. necessary context is perhaps that I'm on 64-bit Windows 7 (my Eclipse install on my Linux laptop works fine)
“Java SE” is three things:
- An abbreviation of “Java Standard Edition”
- A trademark owned by Oracle Corp.
- A set of specifications published by Oracle Corp.
Anybody in the world is free to write software that implements the Java SE specifications. In the past, several companies have done so.
However, anybody in the world is not free to use the trademark of Java. To use that trademark, a person or company is required to come to terms with Oracle in a licensing deal. Presumably that deal would require payment.
Long story short, and over-simplified for brevity… Some of the companies that previously wrote their own implementations of Java SE decided to join forces, combine their codebases, and publish the whole thing as open-source. These companies included Oracle, IBM, and Apple. Thus was born the OpenJDK project (Wikipedia). Since then, other companies and individuals have joined the project.
The OpenJDK name is a trademark owned by Oracle. However, Oracle has published permission allowing others to use the term with no payment required.
The OpenJDK project published source code to an implementation of the Java SE specifications. The project does not publish built binaries or installers.
Several vendors do publish built binaries or installers for implementations of the Java SE specs. Nearly all of these implementations rely largely, if not entirely, in the OpenJDK source code.
These binaries/installers vendors include, in no particular order:
- Azul Systems
- SAP
- Amazon
- Microsoft
- IBM
- Red Hat
- Oracle
- Adoptium
- BellSoft
… and more.
Most of those built binary or installers products use OpenJDK in their name or in their descriptions, as allowed by Oracle. A few of those products may use the term Java or Java SE with explicit permission from Oracle.
There are other editions of Java technology:
- Java Card (for smart cards, badges, etc.)
- Java ME, or Micro Edition (for constrained devices)
- Java EE, or Enterprise Edition (a wide collection of specifications that run on top of an implementation of the Java SE specs, aimed at developers making software for enterprise oriented users)
The first two, Java Card & Java ME are owned by Oracle. The third, Java EE, was donated by Oracle Corp to the Eclipse Foundation were it is now known as Jakarta EE. Jakarta EE is a collection of specifications, with various vendors publishing implementations.
The term “JDK” refers to Java Development Kit. This kit includes an implementation of the Java SE specs, plus tools to write Java apps. These tools include a compiler.
The term “JRE” refers to Java Runtime Environment. This is a JDK minus some of the software development tools.
The term “JVM” refers to Java Virtual Machine. A JVM is a piece of software that enables a Java-based app to execute at runtime on a particular kind of host computer and operating system. Java apps are platform-agnostic, in other words, are not “native”. So a Java app needs a particular JVM to know how to run on a Mac, on a PC, or on a mainframe.
Every JDK and every JRE contains a JVM.
I think your confusion stems from what Java is. Originally, most languages were like C, where you write code, and it gets compiled to a specific computer architecture/ISA (x86, ARM, whatever).
Java "changed the game" when it came on the market, because it was:
Free (many langs at the time were proprietary)
Enforced object oriented programming style (which all the cool kids were doing at the time)
It added the JVM. The JVM is installed on top of the ISA, it was a piece of middleware that meant that compiled Java code could "run anywhere" (in practice, this isn't strictly true, but it's aside the point)
Anyways, if you just need to run Java programs, you can just install the JVM/JRE (of which the JVM is a component). If you actually need to develop Java programs, you need one of these "editions," which supports more or less features, depending on what you are doing with it. If you're a hobbyist programmer, SE is fine. SE, EE, and ME all include the JRE, JVM and JDK.