How to hide the Navigation bar

Reference:

Hide the Navigation
https://developer.android.com/training/system-ui/navigation.html
Responding to UI Visibility Changes
https://developer.android.com/training/system-ui/visibility.html
Using Immersive Full-Screen Mode
https://developer.android.com/training/system-ui/immersive.html

abstract View

getDecorView() Retrieve the top-level window decor view (containing the standard window frame/decorations and the client's content inside of that), which can be added as a window to the window manager.

SYSTEM_UI_FLAG_VISIBLE                        = 0
SYSTEM_UI_FLAG_HIDE_NAVIGATION   = 0x00000002
SYSTEM_UI_FLAG_IMMERSIVE                 = 0x00000800
SYSTEM_UI_FLAG_IMMERSIVE_STICKY = 0x00001000

Code snippet:

Hide the Navigation:
public void showNavigationBar(boolean showNavigationBar) {
        int flags = View.SYSTEM_UI_FLAG_VISIBLE;
        if (!showNavigationBar) {
            flags |= (View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                    | View.SYSTEM_UI_FLAG_IMMERSIVE
                    | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY);
        }
        getWindow().getDecorView().setSystemUiVisibility(flags);
}

Responding to UI Visibility Changes:
private View mDecorView;
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_disable_home_key_demo);
        mDecorView = getWindow().getDecorView();
        mDecorView.setOnSystemUiVisibilityChangeListener
                (new View.OnSystemUiVisibilityChangeListener() {
                    @Override
                    public void onSystemUiVisibilityChange(int visibility) {
                        // Note that system bars will only be "visible" if none of the
                        // LOW_PROFILE, HIDE_NAVIGATION, or FULLSCREEN flags are set.
                        if ((visibility & View.SYSTEM_UI_FLAG_FULLSCREEN) == 0) {
                           // TODO: The system bars are visible. Make any desired
                            // adjustments to your UI, such as showing the action bar or
                            // other navigational controls.
                        } else {
                            // TODO: The system bars are NOT visible. Make any desired
                            // adjustments to your UI, such as hiding the action bar or
                            // other navigational controls.
                        }
                    }
        });
}