CS 151: Object-Oriented Design September 5 Class Meeting Department of Computer Science San Jose State University Spring 2013 Instructor: Ron Mak mak

CS 151: Object-Oriented DesignSeptember 5 Class Meeting

Department of Computer ScienceSan Jose State University

Spring 2013Instructor: Ron Mak

www.cs.sjsu.edu/~mak

SJSU Dept. of Computer ScienceSpring 2013: September 3

CS 151: Object-Oriented Design© R. Mak

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Class Relationships: Dependency

Class C depends on class D: Some method of C manipulates objects of D Example: Mailbox objects manipulate Message objects.

Dependency is asymmetric. The Message class is not aware of the existence of the

Mailbox class. Therefore, Message objects do not depend on Mailbox

objects.

Loose coupling Minimize the number of dependency relationships. Another way for a design to handle change.

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Class Relationships: Aggregation

Class C aggregates class A: Objects of class C contains objects of class A

over a period of time.

A special case of dependency. The “has-a” relationship. Example: An Inventory object has a list of Instrument

objects.

Multiplicity 1:1 – Example: Each Person object has a single

StreetAddress object. 1:n – Example: Each Inventory object has an array of

multiple Instrument objects.



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Class Relationships: Inheritance

Class C inherits from class S. The “is-a” relationship. All class C objects are special cases of class S objects. Class S is the superclass of class C. Class C is a subclass of class S. An object of class C is an object of class S.

Note Aggregation: A Mailbox object has a Message object. Inheritance: A ForwardedMessage object

is a Message object._



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Class-Responsibilities-Collaborations

An effective technique to discover classes, responsibilities, and relationships.

CRC card is an index card that Describes one class. Lists its responsibilities. Lists its relationship with other classes.

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The CRC Technique



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Example: class Mailbox

The CRC Technique

Mailbox

Responsibilities Relationships

Manage passcode MessageQueue

Manage greeting

Create new message



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1. Write the class name on each index card.

2. Distribute the responsibilities among the classes.

3. Find out their relationships and list all dependencies of each classes.

4. Don't write the methods or instance fields. Just write the responsibilities at a high level language.

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The CRC Technique



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A picture is worth a thousand words!

It is much easier to extract information from a graphical notation than reading a textual document.

Show your design in graphical UML diagrams. UML: Unified Modeling Language

There are several different types of UML diagrams. For now, we’ll use Class diagrams Sequence diagrams State diagrams

UML Diagrams



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A class diagram has three compartments: A class diagram has three compartments:

UML Class Diagram

Class Name

Attributes : types

Methods(parms : types) : return type



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Specify the most important attributes and methods. Specify the most important attributes and methods.

If you have too many attributes in a class, If you have too many attributes in a class, check if you can group them into a new class.check if you can group them into a new class.

Example: Example: You have attributes that are specific to your class.You have attributes that are specific to your class. But you also have name, street, city, state, and zip attributes.But you also have name, street, city, state, and zip attributes. Create a new Create a new AddressAddress class to contain those attributes. class to contain those attributes. Then your class Then your class has anhas an address. address.

UML Class Diagram: Attributes and Methods



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Example UML Class Diagram

Mailbox

newMessages : ArrayList<Message>savedMessages : ArrayList<Message>

add(msg : Message) : booleangetCurrentMessage() : Message



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Relationships among classes using arrows. Relationships among classes using arrows.

UML Class Diagram: Relationships

DependencyDependency

AggregationAggregation

InheritanceInheritance

CompositionComposition

AssociationAssociation

Direct associationDirect association

Interface implementationInterface implementation



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Multiplicity in a “has” relationship. Multiplicity in a “has” relationship.

UML Class Diagram: Multiplicities



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UML Class Diagram: Aggregation

Aggregation A “has a” relationship.A “has a” relationship. The contained object The contained object cancan have an existence have an existence

independent of its container.independent of its container.

ExampleExample A mailbox A mailbox has ahas a set of messages. set of messages. A message A message cancan exist without a mailbox. exist without a mailbox. Therefore, a mailbox Therefore, a mailbox aggregatesaggregates messages. messages.

Mailbox Message11 **



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UML Class Diagram: Composition

Mailbox MessageQueue11 11

Composition A “has a” relationship.A “has a” relationship. The contained object The contained object cannotcannot (logically) have an existence (logically) have an existence

independent of its container.independent of its container.

ExampleExample A mailbox A mailbox has ahas a message queue. message queue. The message queue The message queue cannotcannot (logically) exist without a mailbox. (logically) exist without a mailbox. Therefore, a mailbox Therefore, a mailbox composescomposes a message queue. a message queue.



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A class diagram is static. It shows the classes that exist

throughout the lifetime of the system.

A sequence diagram shows the dynamic relationships among the classes at run time. It describes interaction among objects over time during run time.

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UML Sequence Diagram



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Customer

Withdraw cash Keypad Bank AccountDisplay

selectnotify

display confirmation

enter amount

notifyverify

acceptnotify

display bank adsnotify

dispense cash

TIME

Withdraw Cash Sequence Diagram




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Use underlined font for object names to distinguish between class and object names.

The dashed vertical lines are lifelines. A rectangle on a lifeline is an activation bar.

It shows when a object has control executing a method.

The activation bar ends when the method returns. The horizontal arrows are call arrows. Use a sequence diagram to illustrate

complex interactions among a set of objects. Don't show loops or branches.

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At run time, the state of an object is characterizedAt run time, the state of an object is characterizedby the values of its fields.by the values of its fields.

In some objects, different states can cause In some objects, different states can cause different behaviors.different behaviors.

Example: A voice mail systemExample: A voice mail system Caller dials voice mail number Caller dials voice mail number the state is "Connected" the state is "Connected" If caller dial a valid extension If caller dial a valid extension the state is "Recording" the state is "Recording"

If in "Recording" state the caller can type in the passcode If in "Recording" state the caller can type in the passcode the state is "Main menu“ the state is "Main menu“__

UML State Diagram



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Connected

Recording

Main menu

Changepasscode

Passcode Entered

Passcode Entered

Hang upHang up

# 3# 3

Passcode Entered

Passcode Entered

Extension Entered

Extension Entered

Hang upHang up

UML State Diagram



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Free UML Design Tools

StarUML: StarUML: http://staruml.sourceforge.net/en/

Violet: Violet: http://horstmann.com/violet/ Dr. Horstmann’s productDr. Horstmann’s product

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The The javadocjavadoc utility creates a set of utility creates a set of HTML pages for your classes. HTML pages for your classes.

It reads specially formatted comments in your code.It reads specially formatted comments in your code. Delimit comments for javadoc by Delimit comments for javadoc by /**/** and and */*/

It copies the first sentence of your comment to a It copies the first sentence of your comment to a summary table.summary table. Write the first sentence carefully.Write the first sentence carefully. It should start with an uppercase letter and end with a period.It should start with an uppercase letter and end with a period.

javadoc



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javadoc

Javadoc comment example:

Method parameter: Method parameter: @param@param paramname explantion paramname explantion

Function return value: Function return value: @return@return explanation explanation

If the method throws an exception:If the method throws an exception:@throws@throws exceptionname explanation exceptionname explanation

/** * Choose the test string with the highest score and return it. * @param sequence the current sequence. * @param store the sequence store. * @return the chosen test string. */private String chooseString(CurrentSequence sequence, SequenceStore store){ ...}



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On the command line: On the command line: javadocjavadoc pathpath/*.java/*.java

You can also run javadoc from within NetBeans or Eclipse._

Run the javadoc Utility

Demo



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Write only the skeletons of your classes.Write only the skeletons of your classes. No implementation initially.No implementation initially. Just include javadoc comments.Just include javadoc comments. The result is an outline summary of your design.The result is an outline summary of your design.

Example:Example:

Program Design and javadoc

/** * Choose the test string with the highest score and return it. * @param sequence the current sequence. * @param store the sequence store. * @return the chosen test string. */private String chooseString(CurrentSequence sequence, SequenceStore store){ // To be implemented.}

Documents

CS 151: Object-Oriented Design September 5 Class Meeting Department of Computer Science San Jose State University Spring 2013 Instructor: Ron Mak mak