1. Data Structures
Lakshmish Ramaswamy

2. Data Structures Representation of data and set of operations
Different data structures permit different operations with different costs
Insertion, deletion are common operations
Goal – Component reuse
Implement once use multiple times
Example – Filing cabinet, Shelf, Drawer

3. Generic Protocol

4. Collection Interface
Represents group of objects called elements of a specific type
Ordered or unordered
Operations
boolean isEmpty()
int size()
boolean add(AnyType x)
boolean contains(Object x)
boolean remove(Object x)
Void clear()
Object[] toArray()
Java.util.Iterator<AnyType> iterator()

5. Core Collection Interfaces
True collections
Can be manipulated as collections
(have collection-view operations)
Java Collections Framework

7. Iterator Pattern Consider a collection of objects stored in an array
How to print the array elements
for(int i = 0; i < (n-1); i++)
System.out.println(v[i]);
i controls the iteration
i ranges from 0 to (n-1) – all elements in the array
i is an iterator

8. Iterator Design
Iterator class encapsulates position inside of a collection
Provides methods to step through elements
for(itr = v.first(); itr.isValid(); itr.advance())
System.out.println(itr.getData())

9. Generic Iterator Interface

10. Sample Iterator

11. Iterator Example

12. Implementation of Iterator Interface

13. Printing Elements of Collection

14. interface List extends Collection
Lists are collections where the elements have an order
Each element has a definite position (first, second, third, …)
Positions are generally numbered from 0
Duplicates may be allowed
methods of List:
Object get(int pos) – return element at position pos
boolean set(int pos, Object elem) – store elem at position pos
boolean add(int pos, Object elem) – store elem at position pos; slide elements at position pos to size( )-1 up one position to the right
Object remove(int pos) – remove item at given position; shift remaining elements to the left to fill the gap; return the removed element
int indexOf(Object o) – return position of first occurrence of o in the list, or -1 if not found
Java Collections Framework

15. ListIterator
The iterator( ) method for a List returns an instance of ListIterator
Can also send listIterator(int pos) to get a ListIterator starting at the given position in the list
ListIterator returns objects in the list collection in the order they appear in the collection
Supports additional methods:
hasPrevious( ), previous( ) – for iterating backwards through a list
set(Object o) – to replace the current element with something else
add(Object o) – to insert an element after the current element
Java Collections Framework

16. Some examples: a.set(i,a.get(j).times(a.get(k))
What is an equivalence of the following expression:
a[i] = a[j].times(a[k])
for List?
a.set(i,a.get(j).times(a.get(k))
Write a method to swap two indexed values in a List.
private static void swap(List a, int i, int j) {
Object tmp = a.get(i);
a.set(i, a.get(j));
a.set(j, tmp); }
Java Collections Framework

17. Some examples: Write a method to randomly shuffle a list (using swap)
public static void shuffle(List list, Random rnd) {
for (int i=list.size(); i>1; i--)
swap(list, i-1, rnd.nextInt(i)); }
Java Collections Framework