1. COMPUTER 2430 Object Oriented Programming and Data Structures I

2. Queue and Stack Queue: First In First Out (FIFO)
Stack: Last in First Out (LIFO) In
Out

3. Queue Implementation // Circular array int front, rear, count;
front points to where the first element is
rear points to where to add next element
(not the last element!)

4. public class Queue {
private Object[] items;
private int front, rear, count;
public Queue( int size )
public boolean isEmpty()
public boolean isFull ()
public void add ( Object x ) throws Exception
public Object remove() throws Exception
} // class Queue

5. items = new Object[N]; front = rear = count = 0;
Queue Class
items = new Object[N]; front = rear = count = 0;
front
rear 4
(N-1) 1 3 2

6. Queue Class Add A Add B front front A A 4 (N-1) 1 B 4 (N-1) 1 3 2 rearA A 4
(N-1) 1 B 4
(N-1) 1 3 2
rear 3 2
rear

7. Queue Class Add C, D Add E front front rear A A 4 (N-1) 1 E B 4 (N-1)
rear A A 4
(N-1) 1 E B 4
(N-1) 1 B D C D C 3 2
rear 3 2

8. Queue Class After a while Remove twice rear rear 4 (N-1) 1 4 (N-1) 1
rear
rear F 4
(N-1) 1 4
(N-1) 1 D
front
front 3 2 3 2

9. public class Queue <E>{
private E[] items;
private int front, rear, count;
public Queue( int size )
public boolean isEmpty()
public boolean isFull ()
public void add ( E x )
// rear = (rear + 1) % items.length;
public E remove()
// front = (front + 1) % items.length; }

10. Queue Method numItems As Implementer
// Returns the number of items in the queue
public int numItems() {
return count; }

11. User Method numItems
// Do not modify the queue public int numItems(Queue q, int qSize) { Queue tq = new Queue(qSize); int num = 0; while ( !q.isEmpty() ) tq.add( q.remove() ); num ++; } while ( !tq.isEmpty() ) q.add( tq.remove() ); return num; Is the 2nd loop necessary?

12. User Method numItems
public int numItems(Queue q, int qSize) ( Queue tq = new Queue(qSize); int num = 0; while ( !q.isEmpty() ) { tq.add( q.remove() ); num ++; } q = tq; // Can we do this? return num; NO! Pass by Value!

13. User Method numItems
public int numItems(Queue q, int qSize) ( Queue tq = new Queue(qSize); int num = 0; while ( !q.isEmpty() ) { tq.add( q.remove() ); num ++; } while ( !tq.isEmpty() ) q.add( tq.remove() ); return num; The 2nd while loop is necessary! Can you do it without tq?

14. User Method numItems
// If array is allowed public int numItems(Queue q, int qSize) ( // Queue tq = new Queue(qSize); Object [] temp = new Object[qSize]; int num = 0; while ( !q.isEmpty() ) { temp[num ++] = q.remove(); } for (int index = 0; index < num; index ++) q.add( temp[index] ); return num;

15. User Method numItems
// If arrays not allowed! public int numItems(Queue q, int qSize) ( Queue tq = new Queue(qSize); int num = 0; while ( !q.isEmpty() ) { tq.add( q.remove() ); num ++; } while ( !tq.isEmpty() ) q.add( tq.remove() ); return num;

16. Special Queue Operations
Remove the second element of the queue
Remove the last element of the queue
Switch two elements of the queue
User vs Implementer

17. Quizz 4
Monday, November 5
10 points
Queue and Exception

18. Lab 8

19. Lab 7
Prog 4