How to exit an Android app programmatically?

Question

I am sure this question has been asked number of times because I read a few. My client wants me to put a button into his app where users can click and exit. I have read this

Answer 1

 @Override
    public void onBackPressed() {
        Intent homeIntent = new Intent(Intent.ACTION_MAIN);
        homeIntent.addCategory( Intent.CATEGORY_HOME );
        homeIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(homeIntent);
    }