Multiple Java versions running concurrently under Windows

We can install multiple versions of Java Development kits on the same machine using SDKMan.

Some points about SDKMan are as following:

1. SDKMan is free to use and it is developed by the open source community.
2. SDKMan is written in bash and it only requires curl and zip/unzip programs to be present on your system.
3. SDKMan can install around 29 Software Development Kits for the JVM such as Java, Groovy, Scala, Kotlin and Ceylon. Ant, Gradle, Grails, Maven, SBT, Spark, Spring Boot, Vert.x.
4. We do not need to worry about setting the _HOME and PATH environment variables because SDKMan handles it automatically.

SDKMan can run on any UNIX based platforms such as Mac OSX, Linux, Cygwin, Solaris and FreeBSD and we can install it using following commands:

$ curl -s "https://get.sdkman.io" | bash  
$ source "$HOME/.sdkman/bin/sdkman-init.sh" 

Because SDKMan is written in bash and only requires curl and zip/unzip to be present on your system. You can install SDKMan on windows as well either by first installing Cygwin or Git Bash for Windows environment and then running above commands.

Command sdk list java will give us a list of java versions which we can install using SDKMan.

Installing Java 8

$ sdk install java 8.0.201-oracle

Installing Java 9

$ sdk install java 9.0.4-open 

Installing Java 11

$ sdk install java 11.0.2-open

Uninstalling a Java version

In case you want to uninstall any JDK version e.g., 11.0.2-open you can do that as follows:

$ sdk uninstall java 11.0.2-open

Switching current Java version

If you want to activate one version of JDK for all terminals and applications, you can use the command

sdk default java <your-java_version>

Above commands will also update the PATH and JAVA_HOME variables automatically. You can read more on my article How to Install Multiple Versions of Java on the Same Machine.

Of course you can use multiple versions of Java under Windows. And different applications can use different Java versions. How is your application started? Usually you will have a batch file where there is something like

java ...

This will search the Java executable using the PATH variable. So if Java 5 is first on the PATH, you will have problems running a Java 6 application. You should then modify the batch file to use a certain Java version e.g. by defining a environment variable JAVA6HOME with the value C:\java\java6 (if Java 6 is installed in this directory) and change the batch file calling

%JAVA6HOME%\bin\java ...

I was appalled at the clumsiness of the CLASSPATH, JAVA_HOME, and PATH ideas, in Windows, to keep track of Java files. I got here, because of multiple JREs, and how to content with it. Without regurgitating information, from a guy much more clever than me, I would rather point to to his article on this issue, which for me, resolves it perfectly.

Article by: Ted Neward: Multiple Java Homes: Giving Java Apps Their Own JRE

With the exponential growth of Java as a server-side development language has come an equivablent exponential growth in Java development tools, environments, frameworks, and extensions. Unfortunately, not all of these tools play nicely together under the same Java VM installation. Some require a Servlet 2.1-compliant environment, some require 2.2. Some only run under JDK 1.2 or above, some under JDK 1.1 (and no higher). Some require the "com.sun.swing" packages from pre-Swing 1.0 days, others require the "javax.swing" package names.

Worse yet, this problem can be found even within the corporate enterprise, as systems developed using Java from just six months ago may suddenly "not work" due to the installation of some Java Extension required by a new (seemingly unrelated) application release. This can complicate deployment of Java applications across the corporation, and lead customers to wonder precisely why, five years after the start of the infamous "Installing-this-app-breaks-my-system" woes began with Microsoft's DLL schemes, we still haven't progressed much beyond that. (In fact, the new .NET initiative actually seeks to solve the infamous "DLL-Hell" problem just described.)

This paper describes how to configure a Java installation such that a given application receives its own, private, JRE, allowing multiple Java environments to coexist without driving customers (or system administrators) insane...

It is absolutely possible to install side-by-side several JRE/JDK versions. Moreover, you don't have to do anything special for that to happen, as Sun is creating a different folder for each (under Program Files).

There is no control panel to check which JRE works for each application. Basically, the JRE that will work would be the first in your PATH environment variable. You can change that, or the JAVA_HOME variable, or create specific cmd/bat files to launch the applications you desire, each with a different JRE in path.