Software AG Senior Software Developer interview questions

It was on weekend and I attended the interview with moderate preparation. Interview processes looked very quick and fair. But may be because of the position, they expected much. Interview was kind of OK (not too difficult), but they asked some design problems, ALL RELATED TO JAVA. 1st round was taken by two senior persons, and questions asked to me were, 1. design classes and interfaces for Undo/Redo functionality (for example, we see in notepad right, undo redo feature, to simulate that). I was puzzled and using Observer pattern, I gave a probable solution, but they were not convinced. 2. Write program for printing all permutation of string 3. Sort Map based on values 4. Given a NxN matrix and three nodes in it, I need to fill all including nodes with 0 5. Garbage Collection 6. Java Reflection and its uses