Maintaining Multiple instances of an activity

Question

I have an activity that need to be created for 4 different types.

1. Activity User A

2. Activity User B

3. Activity User C

4. Activity User D

All the instances of Activities are created using the same Activity(for example, User) class. Now i want to re order the activity B to top. So from Activity User D im calling the Activity User B using the intent flag FLAG_ACTIVITY_REORDER_TO_FRONT. This is not working. In the logcat its shown,

09-22 18:45:57.028: INFO/ActivityManager(54): Starting activity: Intent { cat=[shoppinglist] flg=0x20000 cmp=com.Sample/.User }

But the activity is not getting displayed(re ordered). Any Help?????

or is there any way if i have the same activity instance with the same type(User B) in the history, i need to finish that instance and create the new one?

Thanks in advance.