Java Collections and Iterators: Storing and Accessing Elements of the Same Type

1. COM S 228 Collections and Iterators Instructor: Ying Cai Department of Computer Science Iowa State University yingcai@iastate.edu Office: Atanasoff 201

2. Java Collection Framework • Very often we need a way to store and access a collection of elements of the same type • A few factors to consider

3. Factors to Considers

4. Factors to Considers

5. Java Collections Framework

6. Key methods of Collection<E> Key methods of Iterator<E>

7. Java Collections Framework

9. foreach loop

10. AbstractCollection<E>

11. An Array-Based Generic Collection

12. Basic data structure Constructors

14. complexity of adding n items?

15. Iterators

16. Iterators

17. Array-based Implementation of FirstCollection Data size: the index of next available slot Iterator Cursor: the index of the item retrieved by next() • hasNext() • next() • remove() checkCapacity() • Advantages • Simple to implement • Disadvantages • A certain amount of memory is required for the array, even when the collection contains few elements • Removing an element requires all elements down to be shifted, making it an O(n) operations

18. Singly-Linked Lists data next

19. We can build a list like this Null-terminated singly-linked list

20. We can access any element by starting at head Mostly, we will use a loop:

21. We can build a list like this Null-terminated singly-linked list

22. Suppose we have this list Now we do this The result is This effectively removes the node containing c

23. Suppose we have this list What happens if we do this

24. Problems with Singly-Linked Lists • Cannot quickly access the predecessor, making it difficult to delete an element • Can only iterate in one direction

25. Doubly-Linked Lists

27. Iterator for Doubly-Linked Lists cursor

28. cursor

29. Iterator Cursor: the index of the item retrieved by next() FirstCollection • hasNext() • next() • remove() Array data Singly-Linked-List Doubly-Linked-List

30. The List Interface A list is a linearly ordered collection with random access to the elements. The List interface extends the Collection interface:

31. List

32. Two ListIterator

33. Two ListIterator

37. We will implement the List interface on top of the Existing class AbstractSequentialList.

38. A Doubly-Linked List Implementation

39. Some helpful methods

40. newNode current

42. A Doubly-Linked List Implementation

43. ListIterator

44. cursor

46. cursor

48. cursor

49. cursor

50. remove() needs to know which direction we’are coming from, AHEAD, BEHIND, or NONE. After it has been called, we have to set direction to NONE, so that it does not get called unless there’s another next() or previous().