public class DatabaseManager {
    static private DatabaseHelper sDbHelper = null;

    static private synchronized DatabaseHelper getInstance(Context c) {
        if (sDbHelper == null)
            sDbHelper = new DatabaseHelper(c.getApplicationContext());
        return sDbHelper;
    }

    static SQLiteDatabase getReadableDb(Context c) {
        DatabaseHelper h = getInstance(c);
        return h.getReadableDatabase();
    }

    static SQLiteDatabase getWritableDb(Context c) {
...

public class ContactsCache {
    static private List<Contact> sContacts == null;

    static public List<Contact> getContacts(Context c) {
        if (sContacts == null)
            sContacts = ContactDao.getContacts(c);
        return sContacts;
    }

    static public void updateContacts(Context c) {
        sContacts = ContactDao.getContacts(c);
    }
}

I'm creating a very simple app for use at the gym that will allow me to select an alarm from a list view and then display the progress as a notification and then plays an alarm sound when the time is up. I want to be able to pull the phone out of my pocket and see the notification on the lock screen showing me how much time I have remaining. I used it at the gym and everything worked great. However, I almost always have music playing at the gym so I wondered what would happen if I didn't have any music playing and tried to use my app. Sure enough the device goes to sleep and my notification stops updating. I looked at various methods of making sure the notification keeps updating even when the phone goes to sleep but none of them worked. I did get it to work using a wakelock and having my app sleep with Thread.sleep(), but that doesn't seem to be an ideal solution. 

I was looking at AlarmService but that doesn't seem to be the right tool and I saw in your book that alarms can't be scheduled for less than 5 seconds out.

The notification doesn't need to be ultra precise, but I'd rather not lose seconds here and there depending on how I'm using the phone.

public class RoamFreeService extends IntentService {
    protected void onHandleIntent(Intent i) {
        get contact name and number from intent
        ContactDao.addContact(this, name);
        ContactsCache.updateContacts(this);

        //display list of contacts with a progress bar next to new contact name;
	// UI fragment will call ContactsCache.getContacts() and display in ListView:
        post contact list refresh event to UI fragment

        // obtain info about new contact received via Rest request
        Contact c = ApiClient.addContact(name, number);
        ContactDao.addContact(this, c);
        ContactsCache.updateContacts(this);

...