1. Lecture 13 Dynamic Collections Richard Gesick
Figures from Lewis, “C# Software Solutions”, Addison Wesley

2. Objectives Review static vs. dynamic collections
Discuss dynamic collection API
Utilize a collection (example)

3. Arrays Allocate a contiguous section of memory Homogeneous
Access via index
<type> NAME[];
NAME = new <type>[SIZE];

4. “Dynamic” Arrays
Arrays are good if you know how large the collection will be
But if this isn’t known beforehand, how big is enough?
One approach:
Allocate for N
When N is exceeded
Allocate 2N and copy N into new space
Free up original space for N
Time consuming (memory allocation/copy)

5. Reallocating an Array
Original
When full A A

6. Reallocating an Array
Original
When full A A B

7. Reallocating an Array
Original
When full A A B

8. Reallocating an Array
Original
When full A A B

9. Reallocating an Array
Original
When full A A B
null

10. Reallocating an Array
Original
When full A
Garbage Collection A B
null

11. Collection APIs Let’s not reinvent the wheel
Other APIs provide access to collections
using System.Collection.Generic;
List – single-reference (one-way) collection
LinkedList – double-reference (two-way)
Queue – first in, first out (FIFO)
Stack – first in, last out (FILO)
Dictionary – key/value pairs
Methods to sort, search, iterate across these collections

12. Focus on List<T>
List provides for growth (dynamic)
Has capacity & count
Capacity = size allocated
Count = number of slots used
Reallocated automatically
Grows when full to 2x
Shrinks when count = ½ capacity (shrinks to 2/3 capacity so we don’t “thrash”)
Provides pseudo-immediate access
Gory details are hidden from us

13. List API List<T>() - Constructor (to hold stuff of type T)
Add(T) - Adds object of type T to end of list
Remove(T) - Deletes first occurrence of match
RemoveAt(int) - Removes the object at position
Sort(…) – arranges the objects
Clear() – removes all objects
Insert(T, int) - Adds object at specified position
Searching:
Contains/Exists/Find/FindAll/FindIndex/FindLast

14. 1301 Asteroids in XNA

15. A Motivating Example Asteroids Game What considerations must be made?
Rocks/asteroids flying around
Ship
Missiles
What considerations must be made?

16. Asteroids Considerations
Collection of rocks
Collection of missiles
Rock - position, velocity
Ship - position, movement, shield
Missile - position, velocity
Collision Detection

17. Summary Array List More details of C# List<T>
Fixed in size (too small/large?)
Immediate access via index
Don’t forget to allocate each element if needed
List
Dynamic in size
Pseudo-immediate access
More details of C# List<T>