UML and Objectorientation. Kristian Sandahl

Transcription

1 UML and Objectorientation Kristian Sandahl

2 2 Maintenance Requirements Validate Requirements, Verify Specification cceptance Test (Release testing) System Design (rchitecture, High-level Design) Verify System Design System Testing (Integration testing of modules) Module Design (Program Design, Detailed Design) Verify Module Design Verify Implementation Module Testing (Integration testing of units) Implementation of Units (classes, procedures, functions) Unit testing Project Management, Software Quality ssurance (SQ), Supporting Tools, Education

3 3 The goals of module design Provide the expected function Prepare for change: Separation of concern Testability Understandability Contribute to quality, eg: Performance Usability Reliability... Map for the implementers and testers

4 4 Modelling software Models supplement natural language Models support both elicitation and design The boundaries between specification and design have to be decided There are high transition costs from functional to object-oriented models UML has become the standard notation Industry interest in SySML (watch out in the future)

5 5 Single Class Class name attributes operations visibility + public - private # protected ~ package Customer name: String[1] String [0..2] +getnooforders():integer +getorderstatus():string + add ( string) Parameter Return type Multiplicity 1 exactly one 0..1 Zero or one * Zero or more (same as 0..*) 2..8 etween 2 and 8

6 Relationships (1/6) - overview and intuition - ssociation 6 ssociation (with navigability)

7 Relationships (1/6) - overview and intuition - ssociation attributes ooktitle + neworderdate: Date [0..1] + islatestedition: oolean [1] + items: ookitem[*] oth representations are almost equivalent 7 role name Date + neworderdate 0..1 * ooktitle * + islatestedition 1 oolean 1 directed association * ookitem + items {ordered} {ordered} {unordered} {unique}{nonunique} Default is unordered, unique

8 class UML-OO/Kristian Sandahl Relationships (1/6) - overview and intuition - ssociation 4 Car Wheel 8 Explicitly show that navigation is not allowed Navigation - mycar can reach the wheels, but not the opposite objects wheel1 mycar wheel2 wheel4 mycar has links to 4 wheels wheel3

9 Relationships (1/6) - overview and intuition - ssociation Car 4 Wheel 9 What does it mean to have a * here? What if we have multiplicity 1 instead? "*" "1" mycar1 mycar2 mycar3 wheel can only be liked to one car instance mycar1 mycar2 wheel1 wheel2 wheel3 wheel4 wheel can be linked to more than one car instance wheel1 wheel2 wheel3 wheel4

10 Relationships (1/6) - overview and intuition - ssociation Car 4 Wheel 10 ssociations are the "glue" that ties a system together association instance = link mycar1 n association describes a relation between objects at run-time. wheel1 wheel2 wheel3 wheel4 {(mycar1,wheel1), (mycar1,wheel2), (mycar1,wheel3), (mycar1,wheel4)}

11 11 Relationships (2/6) - overview and intuition - ggregation ssociation (with navigability) "" has a reference(s) to instance(s) of "". lternative: attributes ggregation

12 Relationships (2/6) - overview and intuition - ggregation Common vague interpretations: "owns a" or "part of" 12 Car 4 Wheel What does this mean? What is the difference to association? Vague definitions Inconsistency and misunderstandings ggregation was added to UML with little semantics. Why? Jim Rumbaugh "Think of it as a modeling placebo" Recommendation: - Do not use it in your models. - If you see it in other's models, ask them what they actually mean.

13 Relationships (3/6) - overview and intuition - Composition 13 ssociation (with navigability) "" has a reference(s) to instance(s) of "". lternative: attributes ggregation void it to avoid misunderstandings Composition

14 Relationships (3/6) - overview and intuition - Composition Car 1 4 Wheel 14 ny difference to association? Yes! First, multiplicity must be 1 or n instance can only have one owner. ut, isn't this equivalent to what we showed with associations? Car 1 4 Wheel mycar1 mycar2 Well, in this case... wheel1 wheel2 wheel3 wheel4

15 Relationships (3/6) - overview and intuition - Composition Using composition Car Wheel MotorCycle Ok for wheels to be part of mycar1 or mybike1 mycar1 mybike1 wheel1 wheel2 wheel3 wheel4 wheel5 wheel6

16 Relationships (3/6) - overview and intuition - Composition Using composition Car Wheel MotorCycle 16 mycar1 Can mycar1 and mybike1 share the same wheels? NO! Not with composition! mybike1 wheel1 wheel2 wheel3 wheel4 Key concepts "No sharing" rule The owner is responsible for managing its parts, wheel5e.g. wheel6 allocation and deallocation.

17 Relationships (3/6) - overview and intuition - Composition Using associations... (Note the difference. The diamond is removed.) Car Wheel MotorCycle Can mycar1 and mybike1 share the same wheels this time? mycar1 Yes! ssociations do not have a "no sharing" rule. mybike1 However, in this case it is a strange model... wheel1 wheel2 wheel3 wheel4 wheel5 wheel6

18 18 Relationships (4/6) - overview and intuition - Generalization ssociation (with navigability) "" has a reference(s) to instance(s) of "". lternative: attributes ggregation void it to avoid misunderstandings Composition n instance of "" is part of an instance of "", where the former is not allowed to be shared. Generalization

19 Relationships - (4/6) overview and intuition - Generalization Class with code for the drive() operation 1. Inheritance ~ relation implementation Vehicle + drive() Vehicle + drive() Car + reverse() Vehicle + drive() 19 Visible Type: Vehicle. Instance of: MotorCycle. Can we drive()? Can we reverse()? Visible Type: Car. Instance of: Car Can we drive()? Can we reverse()? Visible Type: Vehicle. Instance of: Car Can we drive()? Can we reverse()? Car Overrides drive() MotorCycle n instance of a class can have many types = (subtyping) polymorphism + reverse() Inherits the code for drive(). New operation reverse() + drive() 2. Subtyping ~ relation on interfaces static typing: safe substitution

20 Relationships - (5/6) overview and intuition - Realization 20 ssociation (with navigability) "" has a reference(s) to instance(s) of "". lternative: attributes ggregation void it to avoid misunderstandings Composition n instance of "" is part of an instance of "", where the former is not allowed to be shared. Generalization 1) "" inherits all properties and operations of "". 2) n instance of "" can be used where a instance of "" is expected. Realization

21 Relationships - (5/6) overview and intuition - Realization 21 <<interface>> Door + open() Vehicle + drive() Specifier Realization Can we create an instance of Vehicle? Vehicle + drive() Interface (no implementation) Car Implementation MotorCycle Can we create an instance of nothervehicle? + drive() reverse() + reverse() Correct? + open() Provides the Door interface + drive() Must implement the interface bstract class (Italic) bstract operation nothervehicle + drive() + open()

22 Relationships - (5/6) overview and intuition - Realization What is the difference between an interface and an abstract class? 22 <<interface>> Door + open() Interface nothervehicle + drive() + open() bstract class Cannot contain implementation Non of them can be instantiated Can (but need not to) contain implementation n abstract class with only abstract operations is conceptually the same as an interface

23 Relationships - (6/6) overview and intuition - Realization 23 ssociation (with navigability) "" has a reference(s) to instance(s) of "". lternative: attributes ggregation void it to avoid misunderstandings Composition n instance of "" is part of an instance of "", where the former is not allowed to be shared. Generalization 1) "" inherits all properties and operations of "". 2) n instance of "" can be used where a instance of "" is expected. Realization "" provides an implementation of the interface specified by "". Dependency

24 Relationships - (6/6) overview and intuition - Dependency 24 Schedule viewer Lecture client Dependency supplier <<use>>

25 Relationships - overview and intuition 25 ssociation (with navigability) "" has a reference(s) to instance(s) of "". lternative: attributes ggregation void it to avoid misunderstandings Composition n instance of "" is part of an instance of "", where the former is not allowed to be shared. Generalization 1) "" inherits all properties and operations of "". 2) n instance of "" can be used where a instance of "" is expected. Realization "" provides an implementation of the interface specified by "". Dependency "" is dependent on "" if changes in the definition of "" causes changes of "".

26 26 Software Design Patterns Design Pattern is a standard solution for a standard design problem in a certain context. Goal: reuse design information

27 Example: Facade 27

28 Example: Facade 28 Facade

29 29 How to describe design patterns? GoF book

30 30 Facade Intent Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. Motivation Structuring a system into subsystems helps reduce complexity. common design goal is to minimize the communication and dependencies between subsystems. example

31 31 Facade pplicability Use the Facade pattern when: you want to provide a simple interface to a complex subsystem. This makes subsystems more reusable and easier to customize. there are many dependencies between clients and the implementation classes of an abstraction. Introduce a facade to decouple the subsystem from other subsystems, thereby promoting subsystem independence and portability. you want to layer your subsystems. Use a facade to define an entry point to each subsystem level.

32 32 Facade Consequences The Facade pattern offers the following benefits: 1. It shields clients from subsystem components, thereby reducing the number of objects that clients deal with and making subsystem easier to use. 2. It promotes weak coupling between subsystem and its clients. Weak coupling lets you vary the components of the subsystem without affecting its clients. 3. It doesn't prevent applications from using subsystem classes if they need to.

33 33 Facade Structure Participants Collaborations Implementation Sample Code Known Uses Related Patterns

34 Observer 34 50% 50% 40% 30% 20% 10% 0% a b c 40% 30% 20% 10% 0% a b c a = 10% b = 30% c = 40%

35 35 Observer pplicability When an abstraction has two aspects, one dependent on the other. When a change to one object requires changing others. When an object should be able to notify other objects without making assumptions about who these objects are.

36 Observer, structure Subject Stock Investor 36 Observer attach(observer) detach(observer) notify() * update() IM subjectstate getstate() setstate() Goldman Sachs observerstate update() ConcreteSubject ConcreteObserver

37 Observer, collaborations 37

38 38 Observer, consequences bstract coupling between Subject and Observer Support for broadcast communication Unexpected updates

39 Strategy Name: Strategy lso known as: Policy Problem: Need to use different variants of the same algorithm in a class Different algorithms will be appropriate at different time. It is hard to add new algorithms and to change existing ones. 39 Example: Input (Plain Text) Cryptographic Module lgorithms: DES ES Output 3DES Intent (from GoF): (cipher text) "Define a family of algorithms, encapsulate each one and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it." RC5

40 Strategy Structure: Reference to a strategy type bstract 40 Context +contextinterface() -strategy * Strategy +algorithminterface() In example: e.g. class Encryptlg In example: Part of crypto module. Holds data, keys etc. ConcreteStrategy +algorithminterface() ConcreteStrategy +algorithminterface() ConcreteStrategyC +algorithminterface() In Example: Implements e.g. algorithm ES E.g. lgdes E.g. lgrc5

41 41 Strategy Suppose we add a new strategy: Storage media: Disc US-stick DVD Cloud. Input (Plain Text) Cryptographic Module Output (Cipher text on media)

42 Two strategies 42 ackup +EncryptInt () +StoreInt() Media +Store() Disc DVD Cloud Encryptlg +Store() +Store() +Store() +Encrypt() ES lgdes lgrc5 +Encrypt() +Encrypt() +Encrypt()

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