The error was in my graduate work which was about game development.I broadcast some messages to the objects(custmers) registered as Observer who would have different behavior when they received the same message,which is also called Observer Pattern. At first the project had done everything right,but the Observer Pattern doesn’t work when I destoryed some observers which wasn’t used.I finally found out that the problem was due to null references.Because I destroyed the unused objects and didn‘t remove the corresponding reference.

The runtime analysis led me in the rigth direction and finally found the problem.

软件测试基础-Homework1