CSC 212 – Data Structures
LECTURE 41:
COURSE REVIEW
Final Exam
 Fri., Dec. 17th from 8AM – 10AM in OM 200
 Plan on exam taking full 2 hours
 If major problem, come talk to me ASAP
 Exam covers material from entire semester
 Open-book & open-note so bring what you’ve got
 My handouts, solutions, & computers are not allowed
 Cannot collaborate with a neighbor on the exam
 Problems will be in a similar style to 2 midterms
Inheritance
 implements & extends used for relationships
 Both imply there exists an IS-A relationship
public class Student extends Person {…}
public class Cat extends Mammal { … }
public class AQ<E> implements Queue<E>{…}
Inheritance
 All Java classes extend exactly 1 other class
 All fields & methods inherited from the superclass
 Within subclass, can access non-private members
 Private methods inherited, but cannot be accessed
 Classes can implement any number of interfaces
 Must implement methods from the interface
Overriding & Hiding
 Subclass can override/overload inherited methods
 Instance’s type determines which method is called
 Parameter list stays the same to override the method
 Overload method by modifying parameter list
 Field in superclass hidden by redeclaring in subclass
 2 fields with the same name now in subclass
 Use the field for variable’s type
Exceptions in Java
 throw an exception when an error detected
 Exceptions are objects - need an instance to throw
 try executing code & catch errors to handle
 try only when you will catch 1 or more exceptions
 Do not need to catch every exception
 If it is never caught, program will crash
 Not a bad thing – had an unfixable error!
 Exceptions listed in methods’ throws clause
 Uncaught exception only need to be listed
 Should list even if thrown by another method
Abstract Methods
 Methods declared abstract cannot have body
 IOU for subclasses which will eventually define it
 abstract methods only in abstract classes
 Cannot instantiate an abstract class
 But could still have fields & (non-abstract) methods
 abstract methods declared by interfaces
 Interfaces cannot declare fields
 public abstract methods only in interfaces
Arrays vs. Linked Lists
 Concrete implementations used to hold data
 Not ADTs
 Arrays are easier to use & provide quicker access
 Also are impossible to grow
 Implementing ADTs harder due to lack of flexibility
 Slower access & more complex to use linked lists
 Implementing ADTs easier with increased flexibility
 Can be singly, doubly, or circularly linked
Stack vs. Queue
Order read if Stack
Order read if Queue
 Access data with Stack in LIFO order
 Last In-First Out is totally unfair (unless always late)
 Data accessed in Queue using FIFO order
 First In-First Out ensures early bird gets the worm
Simplest ADTs
Queue
Stack
Deque
ADT Operations
DEQUE
QUEUE
STACK
addFront()
addLast()
enqueue()
push()
getFront()
getLast()
front()
top()
removeFront()
removeLast()
dequeue()
pop()
Iterators & Iterables
import java.util.Iterator;
import java.lang.Iterable;
public interface Iterator<E> {
E next() throws NoSuchElementException;
boolean hasNext();
void remove() throws UnsupportedOperationException;
}
public interface Iterable<E> {
Iterator<E> iterator();
}
More Iterator & Iterable
 Abstract work in processing with Iterator
Iterable<Integer> myList;
Iterator<Integer> it;
...
for (it = myList.iterator(); it.hasNext(); ) {
Integer i = it.next();
...
}
 Process Iterable objects in an even easier way
...
for (Integer i : myList) {
...
}
IndexList & NodeList
 Collection which we can access all elements
 Add element before an existing one
 Return the 3rd element in List
 Loop over all elements without removing them
 LIST ADTs differ in how they provide access
 INDEXLIST uses indices for absolution positioning
 Can only use relative positions in NODELIST
 All LISTS are ITERABLE
Sequence ADT
 Combines DEQUE, INDEXLIST, & POSITIONLIST
 Includes all methods defined by these interfaces
 Adds 2 methods to convert between systems
 Get Position at index using atIndex(i)
 indexOf(pos) returns index of a Position
Sequence ADT
 Combines DEQUE, INDEXLIST, & POSITIONLIST
 Includes all methods defined by these interfaces
 Adds 2 methods to convert between systems
 Get Position at index using atIndex(i)
 indexOf(pos) returns index of a Position
Trees vs. Binary Trees
 Both represent parent-child relationships
 Both consist of single "root" node & its descendants
 Nodes can have at most one parent
 Root nodes are orphans -- do not have a parent
 All others, the non-root nodes must have parent
 Children not required for any node in the tree
 No limit to number of children for non-binary trees
 2 children for node in binary tree is the maximum
Traversal Methods
 Many traversals, differ in order nodes visited
 Do parent then do each kid in pre-order traversal
Traversal Methods
 Many traversals, differ in order nodes visited
 Do parent then do each kid in pre-order traversal
 Post-order traversal does kids before doing parents
Traversal Methods
 Many traversals, differ in order nodes visited
 Do parent then do each kid in pre-order traversal
 Post-order traversal does kids before doing parents
 Do left kid, parent, then right kid in in-order traversal
Visualization of Tree
Tree
root
size6

Tree
B
B
D
A
C
F
A
D
F
E
C
E
Picturing Linked BinaryTree
BinaryTree
root
BinaryTree
size4

B
A
B
C

D

A

C


D
Priority Queue ADT
 Priority queue uses strict ordering of data
 Values assigned priority when added to the queue
 Priorities used to process in completely biased order
First you get the sugar,
then you get the power,
then you get the women
Priority Queue ADT
 PriorityQueue yet another Collection
 Prioritize each datum contained in the collection
 PQ is organized from lowest to highest priority
 Access smallest priority only sort of like Queue
 min() & removeMin() return priority & value
 Implementation not defined: this is still an ADT
 Remember that organization & order is theoretical only
Priority Queue ADT







order is theoretical only
Entrys in a PriorityQueue
 PriorityQueues use Entry to hold data
 As with Position, implementations may differ
 Entry has 2 items that define how it gets used
 PQ will only use key – the priority given to the Entry
 Value is important data to be processed by program
Sequence-based Priority Queue
 Simplest implementation of a Priority Queue
 Instance of Sequence used to store Entrys
 Many implementations possible for Sequence
 But we already know how to do that, so…
 Assume O(1) access and ignore all other details
 But how to store Entrys in the Sequence?
 Order Entrys by priority within the Sequence
-OR Sequence unordered & searched when needed
Heaps
 Binary-tree based PQ implementation
 Still structured using parent-child relationship
 At most 2 children & 1 parent for each node in tree
 Heaps must also satisfy 2 additional properties
 Parent at least as important as its children
 Structure must form a complete binary tree
2
5
7
9
6
Hints for Studying
 Will NOT require memorizing:




ADT’s methods
Node implementations
Big-Oh time proofs
(Memorizing anything)
Hints for Studying
 You should know (& be ready to look up):





How ADT implementations work (tracing & more)
For each method what it does & what it returns
Where & why each ADT would be used
For each ADT implementations, its pros & cons
How to compute big-Oh time complexity
Studying For the Exam
1.
What does the ADT do?

2.
How is the ADT used?


3.
Where in the real-world is this found?
What are the applications of this ADT?
How is it used and why?
How do we implement the ADT?


Given the implementation, why do we do it like that?
What tradeoffs does this implementation make?
“Subtle” Hint
Final Exam Schedule
 Lab Mastery Exam is:
Tues., Dec. 14th from 2:45PM – 3:45PM in OM 119
 Final Exam is:
Fri., Dec. 17th from 8AM – 10AM in OM 200