From what I understand, virtualenv enables you to have separate library installation paths, effectively separate "virtual" Python installations.

Java doesn't have the concept of a "system-wide installed" library^(*): It always searches the classpath for the libraries to be loaded. Since the classpath can be (and needs to be!) defined for each application, each application can pick-and-choose which libraries and which versions it wants to load.

If you go down one level deeper and have a single application that somehow needs two different versions of the same library at the same time, then you can do even that with some classpath trickery. It can get complicated, but it's definitely possible (OSGi is one example where this is supported, even Tomcat with two separate webapplications does this).

I've seens some references to security in the virtualenv description: Java has a pretty thorough security system built in. In server applications it's often turned off because it's just easier to configure this way, but you can easily configure what exactly a Java application is allowed to do.

^{(*) Almost, there are extensions or extension libraries, but they aren't used a lot and even those can easily be loaded from arbitrary directories.}

I dont know if it ispossible (install JAVA through PIP) my guess is it is not. But what you have done with "pip install install-jdk" is just intalled a Python library called install-jdk. To have this working you need a python script that import this library and call the function who install JAVA. See https://pypi.org/project/install-jdk/

In Runtime.exec(), ensure that the executable being executed is the python interpreter located inside the virtual environment.

For example, if your virtual environment is in /tmp/my-venv, use the following:

Process process = Runtime.getRuntime().exec("/tmp/my-venv/python hello.py");

Or:

Process process = Runtime.getRuntime().exec(new String[] {"/tmp/my-venv/python", "hello.py"});

Your requirement might need a little clarification, but I suspect you can make it work with a ProcessBuilder. Use directory(File) to control the working directory for the command. And inheritIO() to make stdio work "automatically". Never hardcode a user's home folder. You can use System.getProperty(String) to retrieve the home folder.

ProcessBuilder pb = new ProcessBuilder();
pb.directory(new File(System.getProperty("user.home"), "Documents/venv/"));
pb.inheritIO();
try {
    Process p = pb.command("bin/python3.7",
            "lib/python3.7/site-packages/yyy").start();
    p.waitFor();
} catch (Exception e) {
    e.printStackTrace();
}

It might be better to use System.getenv(String) instead of relying on "Documents/venv" to contain the pyvenv root.