The Starbucks for Android app features a basic mobile payment system. Similar to a gift card, you use a credit card to fill up the app with a certain amount of money, and then scan the bar code to complete the purchase. You can also use the app to track the number of stars you've earned in My Starbucks Rewards Stars and even call up a map that will show you how to get to the closest store near you.
The Starbucks app is a free download at the Google Play Store. Install it and java good time.