Introduction to Software Engineering (CEN-4010)

Introduction to Software Engineering (CEN-4010) Instructor: Masoud Sadjadi http://www.cs.fiu.edu/~sadjadi/ Object Design

Acknowledgements Overview: • Dr. Bernd Bruegge • Dr. Allen Dutoit Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Agenda Overview: • Overview of Object Design • Reuse Concepts • Inheritance and Delegation • Components, Frameworks, and Libraries • System and Object Design Document • JavaDoc and Packaging • Summary Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Object Design Overview: • Object design • is the process of adding details to the requirements analysis and making implementation decisions • The object designer must choose among different ways to implement the analysis model with the goal to minimize execution time, memory and other measures of cost. • Requirements Analysis: • Use cases, functional and dynamic model deliver operations for object model • Object Design: • Iterates on the models, in particular the object model and refine the models • Object Design serves as the basis of implementation Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Object Design: Closing the Gap Overview: Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

App. vs. Solution Domain Objects Overview: • Application objects • also called domain objects. • represent concepts of the domain that are relevant to the system. • They are identified by the application domain specialists and by the end users. • Solution objects • represent concepts that do not have a counterpart in the application domain. • They are identified by the developers. • Examples: Persistent data stores, user interface objects, middleware. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Example Overview: Overview Reuse Concepts Requirements Analysis (Language of Application Domain) Object Design (Language of Solution Domain) Inher., Deleg. Comp., FW, Lib Incident ReportForm Documentation JavaDoc & Pack. Incident Report Summary Text box Menu Scrollbar

Refining App. Domain Objects Overview: • New objects are often needed during object design: • The use of design patterns introduces new classes • The implementation of algorithms may necessitate objects to hold values • New low-level operations may be needed during the decomposition of high-level operations • Example: The EraseArea() operation in a drawing program. • Conceptually very simple • Implementation • Area represented by pixels • Repair () cleans up objects partially covered by the erased area • Redraw() draws objects uncovered by the erasure • Draw() erases pixels in background color not covered by other objects Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Examples of Object Design Activities Overview: • Identification of existing components • Full definition of associations • Full definition of classes • System Design => Service • Object Design => API • Specifying the contract for each component • Choosing algorithms and data structures • Identifying possibilities of reuse • Detection of solution-domain classes • Optimization • Increase of inheritance • Decision on control • Packaging Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Select Subsystem Specification Reuse Identifying missing Identifying components attributes & operations Specifying visibility Adjusting components Specifying types & signatures Identifying patterns Specifying constraints Specifying exceptions Adjusting patterns Object Design Activities (1) Overview: Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Check Use Cases Restructuring Optimization Revisiting Optimizing access inheritance paths Caching complex Collapsing classes computations Delaying complex Realizing associations computations Object Design Activities (1) Overview: Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Reuse Motivation Overview: • Observation about Modeling of the Real World in [Gamma et al 94] • Strict modeling of the real world leads to a system that reflects today’s realities but not necessarily tomorrow’s. • There is a need for reusable and flexible designs. • Design knowledge complements application domain knowledge and solution domain knowledge. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Reuse Heuristics Overview: • Look for existing classes in class libraries • JSAPI, JTAPI, .... • Select data structures appropriate to the algorithms • Container classes • Arrays, lists, queues, stacks, sets, trees, ... • Define new internal classes and operations only if necessary • Complex operations defined in terms of lower-level operations might need new classes and operations Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Reuse Overview: • Main goal: • Reuse knowledge and functionality from previous experience to current problem. • Approaches: Inheritance and Delegation • Inheritance • Interface inheritance • Used for concept classifications  type hierarchies • Implementation inheritance • Used for code reuse. • Delegation • An alternative to implementation inheritance. • Used for code reuse. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Inheritance Object Design Analysis activity Inheritance Taxonomy for Reuse Inheritance detected Inheritance detected Interface Implementation Inheritance by specialization by generalization Inheritance Metamodel for Inheritance Overview: • Inheritance is used to achieve two different goals: Taxonomies and Reuse. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Taxonomy Example Overview: Overview Reuse Concepts Mammal Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary Wale Wolf Tiger

A very similar class is already implemented that does almost the same as the desired class implementation. Example: I have a List class, I need a Stack class. How about subclassing the Stack class from the List class and providing three methods, Push() and Pop(), Top()? Implementation Inheritance Overview: Overview “Already implemented” Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary List Add () Remove() Stack Push () Pop() Top()

Problems Overview: • Problem with implementation inheritance: • Some of the inherited operations might exhibit unwanted behavior. • What happens if the Stack user calls Remove() instead of Pop()? • What happens if the superclass implementation is modified? • The subclass developer is exposed to internal information about the superclass and this may result in tight coupling of subclass to superclass. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Impl. vs Interface Inheritance Overview: • Implementation inheritance • Also called class inheritance • Goal: Extend an application’s functionality by reusing functionality in parent class • Inherit from an existing class with some or all operations already implemented • Interface inheritance • Also called subtyping • Inherit from an abstract class with all operations specified, but not yet implemented Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Delegation Overview: • Delegation • is an alternative to implementation inheritance. • is as powerful as implementation inheritance. • In Delegation two objects are involved in handling a request • A receiving object delegates operations to its delegate. • The developer can make sure that the receiving object does not allow the client to misuse the delegate object. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary Delegate Receiver Client calls Delegates to

List Stack +Add() List +Remove() Remove() +Push() +Pop() +Top() Add() Stack +Push() +Pop() +Top() Delegation vs. Impl. Inheritance Overview: • Inheritance: Extending a base class by a new operation or overwriting an operation. • Delegation: Catching an operation and sending it to another object. • Which of the following models is better for implementing a stack? Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Comparison Overview: • Delegation • Pro: • Flexibility: Any object can be replaced at run time by another one (as long as it has the same type) • Con: • Inefficiency: Objects are encapsulated. • Inheritance • Pro: • Straightforward to use • Supported by many programming languages • Easy to implement new functionality • Con: • Inheritance exposes a subclass to the details of its parent class • Any change in the parent class implementation forces the subclass to change (which requires recompilation of both) Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Reuse Code Overview: • Select existing code • class libraries • frameworks • components • Adjust the class libraries, framework or components • Change the API if you have the source code. • Use the adapter or bridge pattern if you don’t have access • What are the differences among class libraries, frameworks, and components? • They are all composed of a set of related classes. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Frameworks Overview: • A framework is a reusable partial application that can be specialized to produce custom applications. • Frameworks are targeted to particular technologies, such as data processing or cellular communications, or to application domains, such as user interfaces or real-time avionics. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Key Benefits Overview: • Reusability • leverages of the application domain knowledge and prior effort of experienced developers . • Extensibility • is provided by hook methods, which are overwritten by the application to extend the framework. • Hook methods systematically decouple the interfaces and behaviors of an application domain from the variations required by an application in a particular context. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Classification of Frameworks Overview: • White-Box Frameworks • Extensibility achieved through inheritance and dynamic binding. • Existing functionality is extended by subclassing framework base classes and overriding predefined hook methods • Often design patterns such as the template method pattern are used to override the hook methods. • Black-Box Frameworks • Extensibility achieved by defining interfaces for components that can be plugged into the framework. • Existing functionality is reused by defining components that conform to a particular interface • These components are integrated with the framework via delegation. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Another Classification of Frameworks Overview: • Infrastructure frameworks • aim to simplify the software development process • System infrastructure frameworks are used internally within a software project and are usually not delivered to a client. • Middleware frameworks • are used to integrate existing distributed applications and components. • Examples: MFC, DCOM, Java RMI, WebObjects, WebSphere, WebLogic Enterprise Application [BEA]. • Enterprise application frameworks • are application specific and focus on domains • Example domains: telecommunications, avionics, environmental modeling, manufacturing, financial engineering, enterprise business activities. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Class libraries and Frameworks Overview: • Class Libraries: • Less domain specific • Provide a smaller scope of reuse. • Class libraries are passive; no constraint on control flow. • Framework: • Classes cooperate for a family of related applications. • Frameworks are active; affect the flow of control. • In practice, developers often use both: • Frameworks often use class libraries internally to simplify the development of the framework. • Framework event handlers use class libraries to perform basic tasks (e.g. string processing, file management, numerical analysis…. ) Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Components and Frameworks Overview: • Components • Self-contained instances of classes. • Plugged together to form complete applications. • Defines a cohesive set of operations • Can be used based on the syntax and semantics of the interface. • Components may even be reused on the binary code level. • The advantage is that applications do not always have to be recompiled when components change. • Frameworks: • Often used to develop components. • Components are often plugged into black-box frameworks. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Documenting the System Design Overview: • Purpose • System design is documented in the System Design Document (SDD). It describes design goals set by the project, subsystem decomposition (with UML class diagrams), hardware/software mapping (with UML deployment diagrams), data management, access control, control flow mechanisms, and boundary conditions. The SDD is used to define interfaces between teams of developers and serve as a reference when architecture-level decisions need to be revisited. • Audience • The audience for the SDD includes the project management, the system architects (i.e., the developers who participate in the system design), and the developers who design and implement each subsystem. • Template • http://wwwbruegge.in.tum.de/OOSE/SystemDesignDocumentTemplate Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

SDD Template Overview: Outline • Introduction 1.1 Purpose of the system 1.2 Design goals 1.3 Definitions, acronyms, and abbreviations 1.4 References 1.5 Overview • Current software architecture • Proposed software architecture • Overview • Subsystem decomposition • Hardware/software mapping • Persistent data management • Access control and security • Global software control • Boundary conditions • Subsystem services Glossary Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Documenting the Object Design Overview: • Purpose • Object design is documented in the Object Design Document (ODD). It describes object design trade-offs made by developers, guidelines they followed for subsystem interfaces, the decomposition of subsystems into packages and classes, and the class interfaces. The ODD is used to exchange interface information among teams and as a reference during testing. • Audience • The audience for the ODD includes system architects (i.e., the developers who participate in the system design), developers who implement each subsystem, and testers. • Template • http://wwwbruegge.in.tum.de/OOSE/ObjectDesignDocumentTemplate Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

ODD Template (1) Overview: Outline • Introduction • Object design trade-offs e.g., buy vs. build, memory space vs. response time • Interface documentation guidelines e.g., naming conventions, boundary cases, exception handling mechanisms • Definitions, acronyms, and abbreviation • References • Packages describes the decomposition of subsystems into packages and the file organization of the code. This includes an overview of each package, its dependencies with other packages, and its expected usage.3. • Class interfaces Glossary Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Alternative Approaches for ODD Overview: • Self-Contained ODD generated from model • Write and maintain a UML model and generate the document automatically • con: redundancy with the RAD and source code, hard to maintain consistency. • ODD as extension of the RAD • The set of application objects augmented with solution objects. • pro: easier to maintain consistency with the RAD. • con: polluting the RAD with irrelevant information for the user and client, also it may not be possible. • ODD embedded into source code • represent the ODD using a modeling tool. • Once it becomes stable, generate class stubs. • Complete the source code and comments. • Generate the ODD using a tool such as JavaDoc. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Analysis Document Analysis model RAD analysis System design Design goals Object design Initial object design model Generate class stubs Initial class stubs Implementation Document Commented code ODD object design Embedded ODD approach Overview: Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Subsystem decomposition Summary

JavaDoc Overview: • Add documentation comments to the source code. • A doc comment consists of characters between /** and */ • When JavaDoc parses a doc comment, leading * characters on each line are discarded. First, blanks and tabs preceding the initial * characters are also discarded. • Doc comments may include HTML tags • Example of a doc comment: /** * This is a <b> doc </b> comment */ Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

More on JavaDoc Overview: • Doc comments are only recognized when placed immediately before class, interface, constructor, method or field declarations. • When you embed HTML tags within a doc comment, you should not use heading tags such as <h1> and <h2>, because JavaDoc creates an entire structured document and these structural tags interfere with the formatting of the generated document. • Class and Interface Doc Tags • Constructor and Method Doc Tags Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Class and Interface Doc Tags Overview: @author name-text • Creates an “Author” entry. @version version-text • Creates a “Version” entry. @see classname • Creates a hyperlink “See Also classname” @since since-text • Adds a “Since” entry. Usually used to specify that a feature or change exists since the release number of the software specified in the “since-text” @deprecated deprecated-text • Adds a comment that this method can no longer be used. Convention is to describe method that serves as replacement • Example: @deprecated Replaced by setBounds(int, int, int, int). Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Constructor and Method Doc Tags Overview: • Can contain @see tag, @since tag, @deprecated as well as: @param parameter-name description Adds a parameter to the "Parameters" section. The description may be continued on the next line. @return description Adds a "Returns" section, which contains the description of the return value. @exception fully-qualified-class-name description Adds a "Throws" section, which contains the name of the exception that may be thrown by the method. The exception is linked to its class documentation. @see classname Adds a hyperlink "See Also" entry to the method. Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Example of a Class Doc Comment Overview: /** * A class representing a window on the screen. * For example: * <pre> * Window win = new Window(parent); * win.show(); * </pre> * * @author Sami Shaio * @version %I%, %G% * @see java.awt.BaseWindow * @see java.awt.Button */ class Window extends BaseWindow { ... Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Example of a Method Doc Comment Overview: /** * Returns the character at the specified index. An index * ranges from <code>0</code> to <code>length() - 1</code>. * * @param index the index of the desired character. * @return the desired character. * @exception StringIndexOutOfRangeException * if the index is not in the range <code>0</code> * to <code>length()-1</code>. * @see java.lang.Character#charValue() */ public char charAt(int index) { ... } Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Example of a Field Doc Comment Overview: • A field comment can contain only the @see, @since and @deprecated tags /** * The X-coordinate of the window. * * @see window#1 */ int x = 1263732; Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Example: Specifying a Service Overview: /** Office is a physical structure in a building. It is possible to create an instance of a office; add an occupant; get the name and the number of occupants */ public class Office { /** Adds an occupant to the office */ * @param NAME name is a nonempty string */ public void AddOccupant(string name); /** @Return Returns the name of the office. Requires, that Office has been initialized with a name */ public string GetName(); .... } Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Package it all up Overview: • Pack up design into discrete physical units that can be edited, compiled, linked, reused • Construct physical modules • Ideally use one package for each subsystem • System decomposition might not be good for implementation. • Two design principles for packaging • Minimize coupling: • Classes in client-supplier relationships are usually loosely coupled • Large number of parameters in some methods mean strong coupling (> 4-5) • Avoid global data • Maximize cohesion: • Classes closely connected by associations => same package Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Packaging Heuristics Overview: • Each subsystem service is made available by one or more interface objects within the package • Start with one interface object for each subsystem service • Try to limit the number of interface operations (7+-2) • If the subsystem service has too many operations, reconsider the number of interface objects • If you have too many interface objects, reconsider the number of subsystems • Difference between interface objects and Java interfaces • Interface object :Used during requirements analysis, system design and object design. Denotes a service or API • Java interface: Used during implementation in Java (A Java interface may or may not implement an interface object) Overview Reuse Concepts Inher., Deleg. Comp., FW, Lib Documentation JavaDoc & Pack. Summary

Introduction to Software Engineering (CEN-4010)