Executing another java app from an already running one

You can either invoke the program entry point (the “main” function) of the other
application:

public class App1 {
   public void main(String args[]) {

      String []args2 = { "firstparam", "secondparam" };

      App2.main(args2);

   }
}

This will run App2 in the currently running JVM. You could also have the
new application running in another instance of a VM:

public class App1 {
   public void main(String []args) {
      
      Runtime.exec("java App2 firstparam secondparam");

   }
}