Check out example codes for "android studio remove navigation bar". It will help you in understanding the concepts better.

Code Example 1

protected void onResume() {
        View decorView = getWindow().getDecorView();
        // Hides the status and navigation bar until the user clicks
        // on the screeen.
        int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_FULLSCREEN;

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