1. Queues, Deques, and Priority Queues Chapter 22

2. 2 Chapter Contents Specifications for the ADT Queue Using a Queue to Simulate a Waiting Line The Classes WaitLine and Customer Using a Queue to Compute the capital Gain in a Sale of Stock The Classes StockLedger and StockPurchase Specifications of the ADT Deque Using a Deque to Compute the Capital Gain in a Sale of Stock Specifications of the ADT Priority Queue Using a Priority Queue to Compute the Capital Gain in a Sale of Stock

3. 3 Specifications for the ADT Queue Queue organizes entries according to order of entry Exhibits first-in, first-out behavior Contrast to stack which is last-in, first-out All additions are at the back of the queue Front of queue has items added first

4. 4 Specifications for the ADT Queue Fig. 22-1 Some everyday queues.

5. 5 Specifications for the ADT Queue Interface for a queue of objects public interface queueInterface {/** Task: Adds a new entry to the back of the queue. * @param newEntry an object to be added */ public void enqueue(Object newEntry); /** Task: Removes and returns the front of the queue. * @return either the object at the front of the queue or null if the queue was empty */ public Object dequeue(); /** Task: Retrieves the front of the queue. * @return either the object at the front of the queue or null if the queue is empty */ public Object getFront(); /** Task: Determines whether the queue is empty. * @return true if the queue is empty */ public boolean isEmpty(); /** Task: Removes all entries from the queue. */ public void clear(); } // end queueInterface

6. 6 Specifications for the ADT Queue Fig. 22-2 Queue of strings after (a) enqueue adds Jim; (b) Jess; (c) Jill; (d) Jane; (e) Joe; (f) dequeue retrieves, removes Jim; (g) enqueue adds Jerry; (h) dequeue retrieves, removes Jess.

7. 7 Using a Queue to Simulate a Waiting Line Fig. 22-3 A line, or queue of people.

8. 8 Classes WaitLine and Customer Fig. 22-4 A CRC card for the class WaitLine.

9. 9 Classes WaitLine and Customer Fig. 22-5 A diagram of the classes WaitLine and Customer.

10. 10 Classes WaitLine and Customer Fig. 22-6 A simulated waiting line … continued →

11. 11 Classes WaitLine and Customer Fig. 22-6 (ctd) A simulated waiting line.

12. 12 Using a Queue to Compute Capital Gain in a Sale of Stock Must sell stocks in same order they were purchased Must use the difference in selling price and purchase price to calculate capital gain We use a queue to Record investment transactions chronologically Compute capital gain of the stock

13. 13 Classes StockLedger and StockPurchase Fig. 22-7 A CRC card for the class StockLedger

14. 14 Classes StockLedger and StockPurchase Fig. 22-8 A diagram of the class StockLedger and StockPurchase.

15. 15 Classes StockLedger and StockPurchase Fig. 22-9 A queue of (a) individual shares of stock; (b) grouped shares.

16. 16 Specifications of the ADT Deque A Double ended queue Has operations that Add, remove, or retrieve entries At both its front and back Combines and expands the operations of queue and stack

17. 17 Specifications of the ADT Deque Fig. 22-10 An instance of a deque.

18. 18 Specifications of the ADT Deque A Java interface public interface DequeInterface {public void addToFront(Object newEntry); public void addToBack(Object newEntry); public Object removeFront(); public Object removeBack(); public Object getFront(); public Object getBack(); public boolean isEmpty(); public void clear(); } // end DequeInterface

19. 19 Specifications of the ADT Deque Fig. 22-11 A comparison of the operations that add, remove, and retrieve the entries of a stack s, queue q, and a deque d ; (a) add; (b) remove; (c) retrieve.

20. 20 Using a Deque to Compute Capital Gain in Sale of Stock Revise the class StockPurchase Represents purchase of n shares at d dollars per share Constructor is changed Accessor methods for new fields added Revise class StockLedger Method ledger now an instance of a deque Method buy now creates instance of StockPurchase, places it at back of deque Method sell also altered

21. 21 Specifications of the ADT Priority Queue Organizes objects according to priorities Contrast to regular queue in order of arrival Priority queue example – a hospital ER Priority can be specified by an integer Must define whether high number is high priority or … Low number (say 0) is high priority Other objects can specify priority Object must have a compareTo method

22. 22 Specifications of the ADT Priority Queue public interface PriorityQueueInterface {public void add(Comparable newEntry); public Comparable remove(); public Comparable get(); public boolean isEmpty(); public int getSize(); public void clear(); } // end PriorityQueueInterface

23. 23 Using Priority Queue to Compute Capital Gain in Sale of Stock Revise class StockPurchase Include data field date Method compareTo is made available This field is the priority – earliest date is highest priority