Answer Android Calls

I am trying to answer an incoming phone call on android 5.0. I made a native (i.e., Java-only) test project and it worked! But when I call the same code from Qt, nothing happens despite a Process exit code of 0 (indicating success). Here is an excerpt of the relevant code:

Code:

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new Thread(new Runnable() {
                public void run() { 
                    try {
                        Process p = new ProcessBuilder("input", "keyevent",Integer.toString(KeyEvent.KEYCODE_HEADSETHOOK)).start();
                        p.waitFor(); // if I don't do this, I get a java.lang.IllegalThreadStateException
                        System.out.println("exitValue: " + p.exitValue()); //returned: 0
                        System.out.println("error: " + p.getErrorStream()); // returned: java.lang.ProcessManager$ProcessInputStream@2548dfca
                    } catch (Exception e) {
                       e.printStackTrace();
                    }
       }

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I thought that maybe this was a Qt/Android threading issue, but according to my reading, calling Java from a JNI object should take care of that. Does anybody have any insight as to why my call is not answered?

Thank you very much!