Check out example codes for "java get command line output". It will help you in understanding the concepts better.

Code Example 1

private static void GetOutput(final Process process) {
    new Thread() {
        public void run() {
            BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line = null; 
            try {
                while ((line = input.readLine()) != null) {
                    System.out.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }.start();
}

Learn ReactJs, React Native from akashmittal.com