1. CS Week 14
Jim Williams, PhD

2. This Week Final Exam: Conflict Alternatives Emailed
Team Lab: Object Oriented Space Game
BP2 Milestone 3: Strategy
Lecture: More Classes and Additional Topics

3. BP2 M3 Strategy
Test 1: output test. To pass, you'll need: main, promptUser, readInputFile, pigLatin, reverse(ArrayList<String>), manipulate and display working.
Test 2 - unit test of reverse(String). To pass, you'll need matchCase from Milestone 2 to be working.
Recall P5, actionReverse method, or Lab 10, exercise E has a reverse method.
Test 3 - unit test of pigLatin. To pass, you'll need matchCase from Milestone 2 to be working.

4. Visibility Modifiers For members of a class: public private protected
<package>
Demo

5. Can methodA call methodB?
//classes in different files in same package
class A {
public void methodA() {
B b = new B();
b.methodB(); }
class B {
void methodB() {
yes no
depends
error
try it and see.

6. Can a method outside the package call methodA()?
//classes in different files in same package
class A {
public void methodA() {
B b = new B();
b.methodB(); }
class B {
void methodB() {
yes no
depends
error
try it and see

7. Memory areas
code
static
heap
stack

8. Class (static) variables
class Bug {
private static int count = 0;
private final int id;
Bug() {
id = ++count; }
public String toString() {
return "Bug:" + id;

9. How many Bug instances in list?2
2 copies of reference to 1 bug
none, error, no list 3
ArrayList<Bug> list;
list = new ArrayList<Bug>();
list.add( new Bug());
Bug aBug = new Bug();
list.add( aBug);
list.add( 0, aBug);
import java.util.ArrayList;
class Bug {
private static int count = 0;
private final int id;
Bug() {
id = ++count; }
public String toString() {
return "Bug:" + id;
public class ClassNameHere {
public static void main(String[] args) {
ArrayList<Bug> list = new ArrayList<>();
list.add( new Bug());
Bug aBug = new Bug();
list.add( aBug);
list.add( 0, aBug);
System.out.println( list);

10. class (static) vs instance (non-static)
fields
methods

11. Does this print 0, 1, other or error?
public class Person {
static int count = 0;
private boolean something = false;
Person(boolean something) {
this.something = something;
count++; }
System.out.println( Person.count); //in other class in package 1
other
error
try it and see

12. What will print out? 1 can't access a private field outside the class1
can't access a private field outside the class
error
class Employee {
private static int employeeCount = 0;
private final int id;
Employee() {
this.id = ++employeeCount; }
public static void main(String []args) {
Employee anEmployee = new Employee();
System.out.println( anEmployee.id);
try it and see

13. What is the value of num? num: 10 Stuff.num: 6 Stuff.num: 10
class Stuff {
final static int MAX_VALUE = 10; //allowed BP2
static int num = 6; //NOT allowed in BP2
static void change( int n) {
num = n + 1; }
public static void main( String [] args) {
int num = MAX_VALUE;
change( num);
System.out.println("num:" + num);
System.out.println("Stuff.num:" + Stuff.num);
num: 10
Stuff.num: 6
Stuff.num: 10
Stuff.num: 11
error
try it.

14. A static field means every instance will have the exact same toppings
toppings is a class variable
can be accessed by any method
cannot be changed
class Pizza {
static String toppings;
public String getToppings() {
if ( toppings == null)
toppings = "no toppings";
return toppings; }
A, B & C are true
D is false since toppings would have to be 'final' to not be changed.

15. setToppings is a class method can change toppings (write access)
is a setter
is a mutator
class Pizza {
private String toppings;
public void setToppings( String tops) {
if ( tops != null && tops.length() > 0)
toppings = tops; }
B, C and D are all true.
A is not true as setToppings does not have the 'static' keyword in the header before void.

16. getToppings() is a class method class Pizza { can access toppings
cannot access toppings
will not compile
class Pizza {
private String toppings;
public static String getToppings() {
if ( toppings == null)
toppings = "no toppings";
return toppings; }
A, C and D are true
B is false.

17. More Classes
derived classes, overriding member methods, the Object class, polymorphism, ArrayLists of Objects, is-a vs has-a relationships.

18. Class Diagram
Shows structure of a designed system at level of classes.
Independent of time.

19. Animals in Zoo

20. Object Diagram A snapshot of a system at a point in time.
Instances of classes with specific attribute values.

21. Bike Design a bike class. Instance Fields: numWheels, Color, unique id
Class Field: numBikesCreated, used to assign unique id’s to each bike.
Constructor: numWheels and Color, automatically sets the unique identifier.
Instance Methods: Number of Wheels and id can be accessed but not changed. Color can be changed. Add a toString() method to return all instance field values in String form.
Class Method: returns the number of bikes created.
Draw the UML diagram and then write the code.
Create a BikeShop class that creates 10 bikes and stores in an array.
Print out each bike’s number of wheels, color and id using the toString method.

22. Some Useful Classes
Map
Properties

23. Recall Fibonacci Sequence…
Each is the sum of the previous 2.

24. Iterative solution public static void main(String[] args) {
int n = 10;
int [] fib = new int[n];
fib[0] = 1;
fib[1] = 1;
for (int i = 2; i < n; i++) {
fib[i] = fib[i-1] + fib[i-2]; }
System.out.println("fib "+n+"= " + fib[n-1]); {

25. How many times is fib method called?1 3 9
Error
static int fib(int num) {
if ( num <= 1) return 1;
else return fib( num -1) + fib( num -2); }
public static void main(String[] args) {
System.out.println("fibonacci 4: " + fib(4));
try it.

26. Next Week: Course Review
Tools, Diagrams, Data Types, Operators, Keywords, Control Flow, Structured/Procedural, Object Oriented, Exception Control Flow, User Input/Output, File Input/Output, Commenting, Style, Unit Testing, Best Practices...