Preferences preferences = Preferences.systemRoot();
String strRegTime = preferences.get("regTime", "");

Preferences preferences = Preferences.systemRoot();
preferences.put("regTime", "2013-08-29 14:50:20");
try {
    preferences.flush();
} catch (BackingStoreException e) {
   // TODO Auto-generated catch block
    e.printStackTrace();
}
String strRegTime = preferences.get("regTime", "");