1. Big Java
Chapter 16

2. Advanced Data Structures
Often referred to as the Java Collections Framework….
Set and map data types
Hash tables
Binary trees
Heap
Priority queue

3. Sets Unordered collection Fundamental operations: Reject duplicates
Add an element
Remove an element
Containment test (is object in set?)
List elements (in arbitrary order)
Reject duplicates

4. <<interface>>
Set Implementation
<<interface>>
Set
HashSet
TreeSet

5. Example instantiate with specific implementation.
Advantage: could easily
change implementation,
rest of program stays the
same.
use methods from
interface
could also do:
if (names.contains(“Jane”))
{ … }

6. Example (continued) can use “for each” loop with Sets Nodes are not
necessarily visited
in order inserted!

7. Reading Assignment
Read Quality Tip 16.1 pages How would you feel if you had designed the List interface and ArrayList/LinkedList classes?

8. Maps A map data type keeps associations between keys and values
Cannot contain duplicate keys
Operations include:
put
get
containsKey/containsValue
keySet/values – return all keys/values
size
Java has two implementations: HashMap and TreeMap.

9. Example

10. Hash Table Hash table – can be used to implement sets and maps
Hash function – computes an integer value (hash code) from an object, goal is for different objects to yield different hash codes
int h = obj.hashCode();
hashCode is inherited from Object
Collision – when two or more distinct objects have the same hash code

11. HashSet Author provides HashSet, an extension of AbstractSet
provides a hash table with buckets (linked lists) to hold collisions
possible hash code for string:
final int HASH_MULTIPLER = 31; //prime
int h=0;
for (int i=0; i<s.length(); i++)
h = HASH_MULTIPLIER * h + s.charAt(i);
Can use integer fields directly as hash codes
If hashCode not overridden, Object class computes based on memory location of object. Problem if define equals but not hashCode.

12. Binary Search Tree
Review on your own, pages

13. TreeSet or HashSet?
With a good hash function, hashing is usually faster
Balanced trees (remember those?) can guarantee reasonable performance, HashSet depends entirely on performance of hash function
To use TreeSet, objects being stored must implement Comparable interface
For TreeMap, same requirement for keys
Can supply a Comparator object to TreeSet/TreeMap constructor (takes two objects and returns comparison)
TreeSet is preferable if want to print list of items in order

14. Reading Assignment
Random Fact 16.2, Software Piracy, pages

15. Priority Queue Collects elements which have a priority
Elements inserted in any order, but retrieved according to priority
Java includes PriorityQueue() class
Abstract data class
Often use heap to implement
Heaps covered in 406 (I think)
Heapsort is O(n log(n))

16. Chapter 16 Quick Exercise
Use the HashTable code from the textbook
Can you store objects with the same hash code but different data? Try modifying CoinHashCodePrinter to insert two quarters but initialize them differently (e.g., “a quarter” and “quarter” rather than both “quarter”)
Review the TreeSet and TreeSetTester code. Notice the use of CoinComparator. Modify to use with some other class, such as BankAccount