1. Review for the AP CS Exam
Object Oriented Program Design
Program Design
Read and Understand class specifications and relationships among the classes (has a and is a relationships)
Decompose a problem into classes, define relationships and responsibilities of those classes

2. Program design Top down approach Bottom up approach
Make a list of all of the things that a program must accomplish
Each of those things becomes its own module (perhaps a method or perhaps a class with several methods)
Bottom up approach
Starts with specific, detailed way of achieving something(ie recursive area fill or interacting with a piece of hardware)
Builds program up around that detail

3. Class design Class Design Design and implement a class
Design an interface (remember that an interface has only methods, no data)
Extend a class using inheritance (Design question)
Remember that any class that implements an interface must implement all methods in the interface
Use extends and implements appropriately
declare constructors and methods with
meaningful names
appropriate parameters
appropriate return types (remember constructors do not have return types)

4. Class design Class Design
appropriate declaration of methods as private or public
all data should be private

5. Program Implementation
Classes that fill common needs should be built so they can be reused by other programs. OO design is an important part of program implementation
Implementation Techniques
Encapsulation and information hiding
Procedural abstraction

6. Program Implementation
Programming constructs
Primitives vs references
Remember that references must be associated with an object
Beware of aliasing:when two references point to the same object

7. Floating Point Number Probs
Here is an explanation from borland’s web site;
Round-Off Problems :
One of the problems with floating point numbers is round-off. Round off errors occur when attempting to represent certain numbers in any number base. For example, 1/3 is not exactly representable in base ten, while 1/10th is easily representable. But since we're dealing with computers, we are specifically in base two numbers. As opposed to base ten, 1/10th is not exactly representable in base two. For example, the fractional portions of base two are: 1/2 1/4 1/8 1/16 1/32 1/64 1/ / /512 The numbers 1/2, 1/4, 1/8, all powers of two, are exactly representable in a computer. But since 1/10 lies between 1/8 and 1/16, it is not exactly representable using binary notation. So internally the computer has to decide which fractional binary portions to add together to sum close to 1/10. For example: 1/2 1/4 1/8 1/ /32 1/64 1/ / / this adds up to: which is close to but could easily be rounded to .11 so the computer internal algorithm must try to find another combination of binary fractions which come closer to When it's internal algorithm is satisfied, it will have a number which is CLOSE to 1/10th but not EXACT. This inexactness is known as ROUND-OFF error.

8. Constant Declarations
final double WIDTH = ;
Use these whenever you are using a numeric value that you type several places in a program
Variable declarations
Scope of variables
Shadowing problem: Most local variable gets precedence

9. Method declarations Method declarations
A method’s signature consists of name, parameter types and order of parameters
Overloaded methods have the same name but different parameters
Constructors are often overloaded
What is a static method?a method that does not require an instance of the class to be created
What is a private method?accessible only to class member methods

10. Interface Declarations
Interfaces
A collection of methods that a class must implement
An interface you should know
interface java.lang.Comparable
int compareTo(Object other) // return value < 0 if this is less than other // return value = 0 if this is equal to other // return value > 0 if this is greater than other

11. Interface Declarations
Example
Double x = new Double(1.618);
Double y = new Double( );
//Write a statement that compares x to y and prints out “phi is less than pi”
if (x.compareTo(y) < 0) { System.out.println(“phi is less than pi”); }

12. Math Operators Math ops +,-,/,*,% two types of division
type casting (int) and (double)
Students are expected to understand "truncation towards 0" behavior as well as the fact that positive floating-point numbers can be rounded to the nearest integer as (int)(x + 0.5), negative numbers as (int)(x - 0.5)
Math.abs(double x), Math.sqrt(double x), Math.pow(double base, double exp)

13. Control Control techniques Methods
break; //breaks out of nearest loop or case
conditional (if, if else, switch case optional)
iteration (for and while only required)
recursion
Powerful technique when a method invokes itself
Must have some sort of stopping or base case
Remember to use McCarthy method or something similar to trace
many method calls decrease efficiency

14. For each loop used heavily
The for each loop will probably be used heavily in the exam
ArrayList<String> songs = some list
Write a for each loop to print the songs
for(String s: songs) System.out.println(s);

15. For each loop used heavily
int[] nums = some array of integers
Write a for each loop to find the average as a double
int sum = 0;
for( int x: nums) { sum += x; double avg = (double)sum/nums.length;

16. Program Analysis Program Analysis Testing/Debugging
Test Libraries and Classes in isolation
Identify boundary cases
Understand error handling
ArithmeticException
Divide by zero
IndexOutOfBoundsException
ClassCastException
Attempt to cast to subclass of which it is not an instance
NullPointerException
Needed an object, got the shaft!!!
IllegalArgumentException

17. Analysis of Algorithms
Algo Analysis
Big Oh Notation
Asymptotic growth limit
O(n) linear
O(n2) quadratic (two dim array, nested for)
O(logn) divide and conquer(assume base 2, this is comp sci man!!)
O(1) constant time
O(nlogn) better sorting algo’s including logn= find where this element belongs and n to move each element into position

18. Analysis of Algorithms
Data
Search
Array Unordered
O(n)
Array Ordered
O(log n) -> binary search
ArrayList

19. Data Structures int : 32 bit signed integer
double: 64 bit signed floating point
boolean: true or false

20. Classes and Class Hierarchies
Remember chess piece example
abstract base class with abstract method isValidMove()
abstract Piece
abstract isValidMove
Pawn
isValidMove
Knight
isValidMove
Queen
isValidMove

21. Classes and Class Hierarchies
Children must redefine this method
Example of dynamic binding or late binding
Calls to isValidMove are polymorphic

22. Classes and Class Hierarchies
“Cast down the hierarchy”
Ok to cast from Object to Integer assuming class is an Integer
Ok to cast from piece to pawn if you know the piece is a pawn
Children inherit all methods and classes (but cannot play with ancestor’s private vars and methods)
Also, static methods and vars are one per class

23. One/Two dimensional arrays
Once created a certain size, fixed
use .length, the member var
Use [ ] to access elements starting at 0 …length-1
0 and <length works for boundaries
Use array[0].length for column dimensions
Use r and c for loop control vars for ease of reading
Must create individual objects if array of references

24. ArrayList int size() boolean add(Object x) Object get(int index)
Object set(int index, Object x) // replaces the element at index with x // returns the element formerly at the specified position
void add(int index, Object x) // inserts x at position index, sliding elements // at position index and higher to the right // (adds 1 to their indices) and adjusts size
Object remove(int index) // removes element from position index, sliding elements // at position index + 1 and higher to the left // (subtracts 1 from their indices) and adjusts size

25. Stacks FIFO data structures
Good when you need to untangle some type of operations that have to be suspended and returned to

26. Stack interface public interface Stack {
// postcondition: returns true if stack is empty, false otherwise boolean
isEmpty(); // precondition: stack is [e1, e2, ..., en] with n >= 0 // postcondition: stack is [e1, e2, ..., en, x]
void push(Object x); // precondition: stack is [e1, e2, ..., en] with n >= 1 // postcondition: stack is [e1, e2, ..., e(n-1)]; returns en // throws an unchecked exception if the stack is empty
Object pop(); // precondition: stack is [e1, e2, ..., en] with n >= 1 // postcondition: returns en // throws an unchecked exception if the stack is empty
Object peekTop(); }

27. Strings Keep in mind substring first you want, first you don’t want.
class java.lang.String implements java.lang.Comparable
int compareTo(Object other) // specified by java.lang.Comparable
boolean equals(Object other)
int length()
String substring(int from, int to) // returns the substring beginning at from // and ending at to-1
String substring(int from) // returns substring(from, length())
int indexOf(String s) // returns the index of the first occurrence of s; // returns -1 if not found
Keep in mind substring first you want, first you don’t want.
Also, there is a substring with only one argument, starts at that char and goes to end
substring probably a better idea that charAt, since chars not in subset

28. Math.random() All of the random() calls are made using Math.random()
This gives you a number between 0 and 1(non inclusive) Example, use Math.random() to generate a # for choosing an element from an ArrayList called locations int position = (int)(Math.random()*locations.size());

29. Sorting Quadratic Sorts O(n2) Selection Insertion Bubble
Choose the maximal or minimal element by a loop and then swap that with the current place you are moving through
Minimizes swaps
Insertion
Pick an element, shift everyone out of the way to make room for it (Church pew shuffle)
Bubble
Nested for loops allow one element to “bubble” to the front or back each time

30. Sorting nlogn Sorts Merge
Start breaking up your list into smaller lists and merge them together
Requires temporary storage area of size n for merging into

31. Sorting Sort Best Average Worst Selection O(n2) Insertion Merge
O(nlog n)

32. Thats all folks!!!!
Neo journeyed to the machine city and faced off with Smith
Frodo took the ring to the Mountain of Doom
On May 3, you will accomplish your mission, the APCS exam
It is your purpose!