1. CS 302 Week 9
Jim Williams

2. Note: For this correlation, we can't claim TopHat causes higher midterm score simply because it occurred before midterm. There could be something else (e.g., attendance) that influences both.

3. Mid term Evaluations:
Other Resources
30 min delay

4. This Week Program 3 Pants on Fire
Focus
Partners & Milestone 1 due by Thursday
Objects (Instances) and Classes
Conceptual Level and Code Level

5. Classes and Objects public, private, protected, <package>
accessors (getters),mutators (setters)
state of an object
constructor overloading
this
constructor, no-arg, default

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

7. Can methodA call methodB?
//classes in different files in same package
class A {
public void methodA() {
methodB(); }
class B {
void methodB() {
yes no
depends
error

8. Can a method outside the package call methodA()?
//classes in different files in same package
class A {
public void methodA() {
methodB(); }
class B {
void methodB() {
yes no
depends
error

9. Accessors (getters) class Pizza { private String toppings;
public String getToppings() {
if ( toppings == null)
toppings = "no toppings";
return toppings; }

10. Mutators (setters) class Pizza { private String toppings;
public void setToppings( String tops) {
if ( tops != null && tops.length() > 0)
toppings = tops; }

11. Can a setter also get? yes class Pizza { no private String toppings;
public String setToppings( String tops) {
String previous = toppings;
toppings = tops;
return previous; }
yes no
depends
error

12. Object/Instance State
enum Color {GREEN,YELLOW, RED};
class TrafficLight{
private Color color = Color.RED;
public void change() {
if ( color == Color.GREEN) color = Color.YELLOW;
else if ( color == Color.YELLOW) color = Color.RED;
else color = Color.GREEN; }
public Color getColor() { return color; }
public String toString() { return color.name(); }

13. What variables are used for the state of "instance who's reference is in p"?
class Person {
private static count = 0;
private boolean amHungry = false;
public Person( String name) { } }
public static void main(String []args) {
Person p = new Person("Fred");
count
name
amHungry
error/other

14. this class Picture { private boolean hasFrame;
public Picture( boolean hasFrame) {
this.hasFrame = hasFrame; }

15. Does this print true or false?
class Person {
static count = 0;
private boolean something = false;
boolean getThing(boolean something) {
return this.something; }
Person p = new Person();
System.out.println( p.getThing( true));
true
false
error/other

16. Does this print 0, 1, other or error?
class Person {
static count = 0;
private boolean something = false;
Person(boolean something) {
this.something = something;
count++; }
System.out.println( Person.count); 1
other
error

17. Default Constructor class Person { private String name; }
Can we create an instance?
Person p = new Person();

18. Constructor Overloading
class Person {
private String name;
Person() {
this("no name"); }
Person(String name) {
this.name = name;

19. Constructors
yes - the default, no argument constructor
yes - a really good one. no
error
If there is no constructor in a class is a constructor automatically provided by the compiler?

20. Will the no-argument constructor be provided in this case?
class Cup {
private String contents;
Cup(String contents) {
this.contents = contents; }
yes - there is not a no-arg constructor no
yes - why not?
error

21. More Classes and Objects
class, instance, object
field, attribute, instance variable
toString() instance method, overriding
this, super
printing object