1. CS 200
More Classes
Jim Williams, PhD

2. Week 13 Team Lab: Instantiable Class BP2 Milestone 3 Due Thursday
P7 Due next Thursday
CS 300 Programming II in the future?
Lecture: More Classes, UML Diagrams

3. Class as a template A template for objects/instances.
attributes/fields
accessors/getters
mutators/setters
constructors
this (implicit parameter)
public, private, protected, <package>

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

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

6. 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?
best answer: A, yes - the default, no argument constructor.

7. Will the default constructor be provided in this case?
class Cup {
private String contents;
Cup(String contents) {
this.contents = contents; }
yes no
compile time error
runtime error
try it and see.

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

9. 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.

10. 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

11. More Classes The Object class Derived classes Overriding methods
Polymorphism
ArrayLists of Objects
is-a vs has-a

12. Object class Base class for all other classes
Every class in Java directly or indirectly extends (inherits) from Object.
class Picture { //implicitly extends Object }
class Picture extends Object {

13. Derived Classes Since all classes extend from Object they inherit:
public String toString()
public boolean equals(Object obj)

14. Overriding Replacing inherited methods, may call super class method
class Picture {
@Override //compiler directive
public String toString() {
return "Picture: " +super.toString(); }

15. Equals - What does equals mean?
Depends on the implementation in the class.
class Picture {
public boolean equals(Object obj) {
//what do equal Picture objects mean?
return ???; }

16. Polymorphism (runtime)
At runtime determines the correct method to call based on the actual object.
Object o = new Picture();
System.out.print( o.toString());
Is Object's or Picture's toString method called?

17. ArrayLists of Objects
Demo polymorphism using ArrayList

18. is-a vs has-a Relationships
is-a: inheritance
class Dog extends Animal { }
has-a: composition
class Car {
Engine engine;
Wheel [] wheels; }

19. Shapes Add Circle Class to Shapes program: Field: radius
Constructor: radius is the argument
Methods: getArea(), getCircumference(), toString()
Recall: Area = π * radius * radius; Circumference = π × diameter
Add Circle instances/objects to Shapes
Draw UML Diagrams

20. We will fill the blackboard today with diagrams.
Move closer to the front if you can't clearly see.

21. Lots of Jobs if you understand Programming
Software Developer/Programmer/Software Engineer
Testing/Quality Assurance
Technical Support
Technical Writing
Business/Systems Analyst
Software Architect
Product Manager
Project Manager
Development Manager
Technical Sales
Marketing

22. Analysis and Design Analysis: Understanding the Problem
Design: Preparing a Solution
Diagramming can be useful for both.

23. UML Diagrams Goal in CS 200 is to recognize: Use Case Diagram
Class Diagram
Object Diagram
Activity Diagram/Control Flow

24. UML Diagrams: References
Examples of Diagrams:
Simple Drawing Tool:

25. Use Case Behavior diagram
How external users (actors) interact with the system.

26. Class Diagram
Shows structure of a system with features, constraints and relationships.
Independent of time.

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

28. Activity Diagram (Control Flow)
Behavior diagram
Shows flow of control emphasizing sequence and conditions

29. What Kind of Diagram is this?
Use Case Diagram
Class Diagram
Object Diagram
Activity Diagram/Control Flow

30. What Kind of Diagram is this?
Use Case Diagram
Class Diagram
Object Diagram
Activity Diagram/Control Flow

31. What Kind of Diagram is this?
Use Case Diagram
Class Diagram
Object Diagram
Activity Diagram/Control Flow

32. What Kind of Diagram is this?
Use Case Diagram
Class Diagram
Object Diagram
Activity Diagram/Control Flow