Design Patterns - correction mode

background

1. Sometimes when doing business, the need for business success, the callback function will be operating.
2. For the needs of the scene, how to design it

achieve

1. Task: abstract class, two methods, which use a assigned to the client, a method for performing service operations, the callback function is required. execute () is an abstract method to be implemented subclass
2. SimpleTask: implementation of a specific service logic execution
3. Callback: callback function