1. Fundamentals of Software Development 1
4/19/2019
Today’s Summary
Interfaces
What are they?
Why are they important?
How do they relate to WordGames?
Why classes are important
UML class diagrams
Implementing your own classes
Defining a method
By using documented stubs
Parameters and returned values
Invoking a method
Summarized on the next few slides
Fundamentals of Software Development 1
Rose-Hulman Institute of Technology

2. Why have interfaces?
A Java interface is the “face” that one class shows others
An interface contains the signature but not body for each method
Any class that implements an interface must provide the methods listed in the interface
So an interface specifies a contract
public interface ClockRadio {
public Time getTime();
public void setTime(Time x);
public void setTime(Time x, Station s); }
Example of a Java interface
Fundamentals of Software Development 1

3. UML class diagram for WordGames
All our stuff
The StringTransformable interface is how our code knows how to “connect” to your code
<<interface> StringTransformable
transform(String) : String
Capitalizer
NameDropper
xxx …
xxx
Questions on this important idea?
Fundamentals of Software Development 1

4. Why classes are important
What does an object’s type tell you?
Answer: How the object operates!
What attributes the object has
What operations the object can do
Fact: The type of an object is simply the name of the class to which the object belongs
What can you conclude from the above statements?
Answer: The class (i.e. type) of an object tells you how the object operates!
Questions?
Fundamentals of Software Development 1

5. Review: UML class diagrams
Fundamentals of Software Development 1
4/19/2019
Review: UML class diagrams
What they are
A notation to assist object-oriented design (not just Java)
Why use UML?
UML as sketch
To figure out a design
To communicate ideas and alternatives
UML as blueprint
To convey the design to the coder
UML as programming language
To generate code automatically from the design
This is how we (and most people) use UML class diagrams – as a tool to help our thinking
Fundamentals of Software Development 1
Rose-Hulman Institute of Technology

6. Review: UML class diagrams – relationships-only
is-a (by extending a class)
is-a (by implementing an interface)
has-a
1 means one
* means 0 or more
1 .. * means 1 or more
means 0 or 1
Order
Customer * 1 1
lineItem *
Order Line *
Corporate Customer
Personal Customer 1
Product *
0..1
salesRep
Questions?
Employee
Fundamentals of Software Development 1

7. UML class diagram with details
Fundamentals of Software Development 1
4/19/2019
UML class diagram with details
EyeBall
Together, let’s examine JavaEyes and fill in the details for the EyeBall class in the UML class diagram
What are the attributes? Their types?
Any comments needed?
What are the operations? Their types?
eyeBallColor : Color
xPosition : int
yPosition : int
radius : int
Sets the EyeBall color to the given color
EyeBall(Color eyeBallColor)
draw( Graphics graphics)
look(int x, int y)
Moves the EyeBall to follow the mouse to the given (x, y) point
There are two ways to show an object-type attribute:
Draw a HAS-A arrow to it
List it in the detailed box
Choose the former if you want to emphasize the relationship
Questions?
Fundamentals of Software Development 1
Rose-Hulman Institute of Technology

8. Method invocation versus definition
Fundamentals of Software Development 1
4/19/2019
Method invocation versus definition
“There is a difference between knowing the path and walking the path.” ~ Morpheus
“There is a difference between defining a method and invoking a method.” ~ CSSE Prof.
Fundamentals of Software Development 1
Rose-Hulman Institute of Technology

9. Method invocation versus definition
Fundamentals of Software Development 1
4/19/2019
Method invocation versus definition
To define (write) a method means to write its code
The code is a recipe to follow when the method runs
Methods often have parameters – information that comes into the method when it is run
To invoke (call, run) a method means to cause the method’s code to run
Sending it actual values to substitute for the formal parameters of the method
Example (on next slides)
Fundamentals of Software Development 1
Rose-Hulman Institute of Technology

10. Method invocation versus definition
To define (write) a method means to write its code
To invoke (call, run) a method means to cause the method’s code to run
Example (on next slide):
The NameDropper class in the blue box defines:
A field called myName to hold the NameDropper’s name to drop
A constructor called NameDropper that takes the name to store in the field
A method called transform that takes a phrase to tranform
The statements in the yellow box cause the NameDropper constructor and transform method to run
They each run several times, with different actual arguments substituted for the formal parameters in the NameDropper definition
These statements would themselves appear in some other class
Fundamentals of Software Development 1

11. private String myName;
public class NameDropper extends StringTransformer implements StringTransformable {
private String myName;
public NameDropper(String nameToUse) { this.myName = nameToUse; }
public transform(String phrase) { return this.myName + “says ” + phrase; } }
Definition of the NameDropper class
NameDropper person1, person2, person3;
person1 = new NameDropper(“Calvin”);
person2 = new NameDropper(“Hobbes”);
person3 = new NameDropper(“lobster”);
person1.transform(“you look funny today, Hobbes.”);
person2.transform(“you looker even funnier.”);
person1.transform(“no, YOU look funnier.”);
person3.transorm(“I amd just a lonely lobster.”);
Invoking the NameDropper constructor and transform method
Questions?
Fundamentals of Software Development 1

12. Implementing by using documented stubs
Stub: a method whose body is either:
empty (if the method returns nothing), or
trivial, for example:
return null (if the method returns an object)
return 999 (if the method returns a number)
return true (if the method returns a boolean)
Documented stub: a stub with appropriate Javadoc
Example on next slide
Fundamentals of Software Development 1

13. Implementing by using documented stubs
Stub: a method whose body is either empty or trivial
Documented stub: a stub with appropriate Javadoc
Implementing by using documented stubs
/** * A StringTransformer that transforms the phrase that it is given * by capitalizing it. * David Mutchler. */ public class Capitalizer extends StringTransformer implements StringTransformable {     /**     * Does nothing beyond constructing the Capitalizer.     */     public Capitalizer() {     }     /**     * Capitalizes each letter of the given phrase and return the result.     *     thePhrase The phrase to transform.     The capitalized version of the given phrase.     */     public String transform(String thePhrase) { return null;     } }
Questions?
Stub
Stub, to be filled in later by:
return this.myName + “says ” + phrase;
Fundamentals of Software Development 1

14. What’s Ahead? Before the next session: Next week – Details to follow:
Reminder: Find the homework assignment from the Schedule page of the CSSE 120 Angel site
angel.rose-hulman.edu
What’s Ahead?
Before the next session:
Do Homework 7 (no late homework!)
Including the reading and the associated online quiz
Next session:
More WordGames - Implementing your own classes!
Next week – Details to follow:
Review session Tuesday night
First exam Wednesday night
Our usual suggestion: Routinely do your homework in F-217 (CSSE lab). A student assistant is there every Sunday through Thursday evening, 7 pm to 9 pm, so you can get immediate answers to any questions you might have.
Fundamentals of Software Development 1