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// Ref: https://stackoverflow.com/questions/8644665/how-to-check-the-hdmi-device-connection-status-in-android

private boolean isHdmiSwitchSet() {

    // The file '/sys/devices/virtual/switch/hdmi/state' holds an int -- if it's 1 then an HDMI device is connected.
    // An alternative file to check is '/sys/class/switch/hdmi/state' which exists instead on certain devices.
    File switchFile = new File("/sys/devices/virtual/switch/hdmi/state");
    if (!switchFile.exists()) {
        switchFile = new File("/sys/class/switch/hdmi/state");
    }
    try {
        Scanner switchFileScanner = new Scanner(switchFile);
        int switchValue = switchFileScanner.nextInt();
        switchFileScanner.close();
        return switchValue > 0;
    } catch (Exception e) {
        return false;
    }
}