DeviceUtils.java

public class Utils {

    private static final String UNIQUE_DEVICE_ID = "unique_device_id";
    private static String issuedId;

    public static String getDeviceID(Context context) {

        if (issuedId != null) {
            return issuedId;
        }

        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);

        String id = sharedPreferences.getString(UNIQUE_DEVICE_ID, null);

        if (id == null) {
            id = UUID.randomUUID().toString();
            Utils.issuedId = id;
            sharedPreferences.edit().putString(UNIQUE_DEVICE_ID, id)
                    .apply();
        } else if (issuedId != null) {
            return issuedId;
        }

        return id;
    }
}