Fundamentals of Software Development 1Slide 1 Today’s Summary InterfacesInterfaces –What are they? –Why are they important? –How do they relate to WordGames? Why classes are importantWhy classes are important UML class diagramsUML class diagrams Implementing your own classesImplementing your own classes –Defining a method By using documented stubsBy using documented stubs –Parameters and returned values –Invoking a method Summarized on the next few slides

Fundamentals of Software Development 1Slide 2 Why have interfaces? A Java interface is the “face” that one class shows othersA 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 contractSo an interface specifies a contract public interface ClockRadio { public Time getTime(); public Time getTime(); public void setTime(Time x); public void setTime(Time x); public void setTime(Time x, Station s); public void setTime(Time x, Station s);} Example of a Java interface

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

Fundamentals of Software Development 1Slide 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? The class (i.e. type) of an object tells you how the object operates!Answer: The class (i.e. type) of an object tells you how the object operates! Questions?

Fundamentals of Software Development 1Slide 5 Review: UML class diagrams What they areWhat they are –A notation to assist object-oriented design (not just Java) Why use UML?Why use UML? –UML as sketch To figure out a designTo figure out a design To communicate ideas and alternativesTo communicate ideas and alternatives –UML as blueprint To convey the design to the coderTo convey the design to the coder –UML as programming language To generate code automatically from the designTo 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 1Slide 6 Review: UML class diagrams – relationships-only Order Line Product Corporate Customer OrderCustomer Personal Customer Employee salesRep is-a (by extending a class) is-a (by implementing an interface) has-a 1means one *means 0 or more 1.. *means 1 or more 0.. 1means 0 or 1 lineItem 1 * * * * Questions?

Fundamentals of Software Development 1Slide 7 UML class diagram with details Together, let’s examine JavaEyes and fill in the details for the EyeBall class in the UML class diagramTogether, let’s examine JavaEyes and fill in the details for the EyeBall class in the UML class diagram What are the attributes? Their types?What are the attributes? Their types? –Any comments needed? What are the operations? Their types?What are the operations? Their types? –Any comments needed? EyeBall eyeBallColor : Color xPosition : int yPosition : int radius : int 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 Sets the EyeBall color to the given color Questions?

Fundamentals of Software Development 1Slide 8 Method invocation versus definition “There is a difference between knowing the path and walking the path.” ~ Morpheus“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.“There is a difference between defining a method and invoking a method.” ~ CSSE Prof.

Fundamentals of Software Development 1Slide 9 Method invocation versus definition To define (write) a method means to write its codeTo 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 runTo 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)Example (on next slides)

Fundamentals of Software Development 1Slide 10 Method invocation versus definition To define (write) a method means to write its codeTo define (write) a method means to write its code To invoke (call, run) a method means to cause the method’s code to runTo invoke (call, run) a method means to cause the method’s code to run Example (on next slide):Example (on next slide): –The NameDropper class in the blue box defines: A field called myName to hold the NameDropper’s name to dropA field called myName to hold the NameDropper’s name to drop A constructor called NameDropper that takes the name to store in the fieldA constructor called NameDropper that takes the name to store in the field A method called transform that takes a phrase to tranformA 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 definitionThey 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 classThese statements would themselves appear in some other class

Fundamentals of Software Development 1Slide 11 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; } } 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.”); Definition of the NameDropper class Invoking the NameDropper constructor and transform method Questions?

Fundamentals of Software Development 1Slide 12 Implementing by using documented stubs Stub: a method whose body is either: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 null (if the method returns an object) return 999 (if the method returns a number)return 999 (if the method returns a number) return true (if the method returns a boolean)return true (if the method returns a boolean) Documented stub: a stub with appropriate JavadocDocumented stub: a stub with appropriate Javadoc Example on next slideExample on next slide

Fundamentals of Software Development 1Slide 13 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; } } Stub: a method whose body is either empty or trivial Documented stub: a stub with appropriate Javadoc Stub Stub, to be filled in later by: return this.myName + “says ” + phrase; Questions?

Fundamentals of Software Development 1Slide 14 What’s Ahead? Before the next session:Before the next session: –Do Homework 7 (no late homework!) Including the reading and the associated online quizIncluding the reading and the associated online quiz –Next session: More WordGames - Implementing your own classes!More WordGames - Implementing your own classes! Reminder: Find the homework assignment from the Schedule page of the CSSE 120 Angel site angel.rose-hulman.edu 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.