Where to download JRE 11

There is no JRE in Java 11. If you are a developer, you can run your program using JDK 11. If you want to do this from the command line, you should make sure that the path to java or to java.exe from JDK11 is set, in the environment variable PATH, before the path to java or to java.exe of older JREs. At the same time, you should take into account that in Windows, the installers of the old Public JRE copied java.exe to the C:\Windows\System32 directory, which is also registered in PATH. It's best to just delete the old Public JRE. You don't have to delete the old JDK, it won't hurt.

If you want to send your program to an end user who now does not have a suitable JRE and does not want to install the JDK, you should create a runtime environment (some kind of old JRE) that will include only the necessary Java modules, including the module of your program.

For example, let's analyze a simple Hello world. Let your program consist of a single class com.example.MainClass and is a module tryout, that is, except com/example/MainClass.java you have and module-info.java (in the default package, i.e. above com) with the module description. For example, with the following minimum:

module tryout {
}

By the way, in IntelliJ IDEA, adding a module is a separate operation from adding a class to the New menu. You can't create module-info.java the same way you create a regular class.

After building your project, for example, using Maven, you will get a jar file, the exact name of which is completely unimportant. This is a jar file and will be yours a module whose description will be inside it in module-info.class. To create a runtime environment, you should run something like this command:

jlink --module-path . --add-modules tryout --launcher start=tryout/com.example.MainClass --output tryoutapp

Description of the parameters used:

--module-path . tells you where to look for modules other than JDK modules. In this case, in the current directory ..

--add-modules tryout specifies which modules to include, except for the modules included by default from the JDK.

--launcher start=tryout/com.example.MainClass says that you need to create startup scripts start (UNIX Shell script) and start.bat (Batch script) which will run the tryout module by running the com.example.MainClass class in that module. Specifying the class is optional, and in my case it was necessary because I was too lazy to specify it in MANIFEST.MF inside the jar file.

--output tryoutapp tells you in which directory to create a runtime environment. At the same time, if such a directory already exists and even if it is empty, there will be an error: "Error: directory already exists: tryoutapp".

Eventually you will get the directory tryoutapp inside which will be everything you need to run your program (your module). However, you will not find your jar file there. Your module (and hence the class com.example.MainClass), together with the other modules, will be located in the file tryoutapp/lib/modules. In my case, the size of this file is 23 megabytes. The start scripts start and start.bat will be located in the tryoutapp/bin directory.

You can get a more detailed description of the jlink utility by running jlink --help.