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

Code Example 1

protected void onResume() {
        super.onResume();
        View decorView = getWindow().getDecorView();
        // Hide the status bar.
        int uiOptions = View.SYSTEM_UI_FLAG_FULLSCREEN;
        decorView.setSystemUiVisibility(uiOptions);
    }

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