Object-Oriented Introduction

Transcription

1 Object-Oriented Introduction Or: Your Honor, I Object... Jonathan Sprinkle 1 University of Arizona Department of Electrical and Computer Engineering PO Box , Tucson, AZ 85721, USA August 22, 2012 Jonathan Sprinkle Object-Oriented Introduction 1

2 Abstract Abstract This lecture introduces the Kay criteria of an OO Language. It then provides some formal definitions of various OO Language properties, and discusses the kinds of UML models and diagrams which will become familiar in this course. Additional discussion is devoted to the foundations of class and object diagrams, along with examples. Jonathan Sprinkle Object-Oriented Introduction 2

3 Previously, on ECE Computers created to solve decision (logic) problems, with data stream in, and T/F outputs. Simultaneously evolved into computational engines Machine language created to automate computer construction HLLs created to make programming more like problem solving (and less like machine assembly) Later languages (e.g., C) evolved for purpose of easing compatibility concerns OO emerged from perspective of scalability (c.f. software crisis), and have benefitted distributability as well Jonathan Sprinkle Object-Oriented Introduction 3

4 Outline 1 An Object Oriented Manifesto? What s in an Object? Object-Oriented Definitions 2 Object-Oriented Development Development and Stages of Development 3 Kinds of models Structural Modeling Behavioral Modeling Interaction Modeling 4 The Class Diagram In the beginning... Graphical Notations 5 Inheritance Notation 6 Association Graphical Notations Jonathan Sprinkle Object-Oriented Introduction 4

5 What s in an Object? Tenets of an OO Language (per Alan Kay) 1 Everything is an object. 2 A program is a bunch of objects telling each other what to do by sending messages 3 Each object has its own memory, made up of other objects 4 Every object has a type 5 All objects of a particular type can receive the same message This list is very important. You should commit this list of characteristics of an OO language to memory. Jonathan Sprinkle Object-Oriented Introduction 5

6 What s in an Object? Tenets of an OO Language (per Alan Kay) 1 Everything is an object. 2 A program is a bunch of objects telling each other what to do by sending messages 3 Each object has its own memory, made up of other objects 4 Every object has a type 5 All objects of a particular type can receive the same message This list is very important. You should commit this list of characteristics of an OO language to memory. Jonathan Sprinkle Object-Oriented Introduction 6

7 What s in an Object? Tenets of an OO Language (per Alan Kay) 1 Everything is an object. 2 A program is a bunch of objects telling each other what to do by sending messages 3 Each object has its own memory, made up of other objects 4 Every object has a type 5 All objects of a particular type can receive the same message This list is very important. You should commit this list of characteristics of an OO language to memory. Jonathan Sprinkle Object-Oriented Introduction 7

8 What s in an Object? Tenets of an OO Language (per Alan Kay) 1 Everything is an object. 2 A program is a bunch of objects telling each other what to do by sending messages 3 Each object has its own memory, made up of other objects 4 Every object has a type 5 All objects of a particular type can receive the same message This list is very important. You should commit this list of characteristics of an OO language to memory. Jonathan Sprinkle Object-Oriented Introduction 8

9 What s in an Object? Tenets of an OO Language (per Alan Kay) 1 Everything is an object. 2 A program is a bunch of objects telling each other what to do by sending messages 3 Each object has its own memory, made up of other objects 4 Every object has a type 5 All objects of a particular type can receive the same message This list is very important. You should commit this list of characteristics of an OO language to memory. Jonathan Sprinkle Object-Oriented Introduction 9

10 Object-Oriented Definitions Definition: Object-Oriented Definition Object-Oriented (OO) means that software is organized as a collection of discrete objects which incorporate both data structure and behavior. Four characteristics which any OO language implements include identity, classification, inheritance, and polymorphism. Note: As we mentioned previously, data structure and behavior have not always been tightly coupled. As a classic example, C function calls always require data to be passed in, or must interact with global variables. Jonathan Sprinkle Object-Oriented Introduction 10

11 Object-Oriented Definitions Definition: Identity Definition Identity means that data is quantized into discrete, distinguishable entities called objects. Each object must have its own inherent identity, regardless of its state. Corollary Two objects, a, and b, both of which are instantiated from class C, are distinct even if all attribute values match. A few notes: this is required, since most OO languages are implemented through message passing, More to come on that in future lectures. Jonathan Sprinkle Object-Oriented Introduction 11

12 Object-Oriented Definitions Definition: Classification Definition Classification means that objects with the same data structures (i.e., attributes), and behavior (operations) may be grouped into a class. A class is an abstraction that describes properties that are important, and ignores the rest. Note: A class may describe a (potentially) infinite set of unique objects. Jonathan Sprinkle Object-Oriented Introduction 12

13 Object-Oriented Definitions Definition: Instance Definition An instance is an object that has been created from a class. Instantiation means the creation of an object (instance) from the class. i:c is shorthand for i is an instance of C Note: Instance and Object may be interchangeably used. Note: An object contains an implicit reference to its own class; i.e., it has self-awareness (knows what kind of thing it is). Jonathan Sprinkle Object-Oriented Introduction 13

14 Object-Oriented Definitions Definition: Inheritance Definition Inheritance is the sharing of attributes and operations (together called features) among classes, based on a hierarchical relationship of either subclass or superclass. Features describe the set of collected attributes and operations associated with a class. Jonathan Sprinkle Object-Oriented Introduction 14

15 Object-Oriented Definitions Definition: Super/Sub-class Definition A superclass has a general feature set which must exist for all subclasses. Definition A subclass is a refinement of a class. All features available to the superclass must be available to the subclass. Features that are created for the subclass are not available through the interface of the superclass. IS-A is used to denote a subclasss impersonation of its parent class: A square IS-A rectangle. Jonathan Sprinkle Object-Oriented Introduction 15

16 Object-Oriented Definitions Definition: Attribute Definition An attribute is a class that is contained by an owner class. When the owner class is instantiated, the attribute is an object. Jonathan Sprinkle Object-Oriented Introduction 16

17 Object-Oriented Definitions Definition: Polymorphism Definition Polymorphism means that the same operation may behave differently for different classes. Note: Permissions may be given to inheritance, operations, and attributes, to limit (or permit) interaction from other objects Jonathan Sprinkle Object-Oriented Introduction 17

18 Object-Oriented Definitions Definition: Operation Definition An operation is a procedure or transformation that an object performs or is subject to. An implementation of an operation by a specific class is called a method. Note: Due to inheritance, there may be more than one method that implements a specific operation, one for each of the inheriting classes. Jonathan Sprinkle Object-Oriented Introduction 18

19 Object-Oriented Definitions Definition: State Definition State is a snapshot of the program in its current execution, namely the collection of all states of all objects. Note: If operations are viewed to be atomic, then only attributes can be used to determine an object s state. Jonathan Sprinkle Object-Oriented Introduction 19

20 Object-Oriented Definitions Definition: Encapsulation Definition Encapsulation separates the external aspects/interface of an object from the internal implementation details. Encapsulation is also called information hiding. Jonathan Sprinkle Object-Oriented Introduction 20

21 Outline 1 An Object Oriented Manifesto? What s in an Object? Object-Oriented Definitions 2 Object-Oriented Development Development and Stages of Development 3 Kinds of models Structural Modeling Behavioral Modeling Interaction Modeling 4 The Class Diagram In the beginning... Graphical Notations 5 Inheritance Notation 6 Association Graphical Notations Jonathan Sprinkle Object-Oriented Introduction 21

22 Development and Stages of Development Definition: Development Definition Development refers to the software life-cycle: analysis, design, implementation, and maintenance. Important distinction for the emerging area of systems modeling: the same tools and notation can be used for analysis, design, and implementation modeling artifacts serve as documentation for the systems maintenance, and for refinement of the system as it is maintained Jonathan Sprinkle Object-Oriented Introduction 22

23 Development and Stages of Development Definition: Development Definition Development refers to the software life-cycle: analysis, design, implementation, and maintenance. Important distinction for the emerging area of systems modeling: the same tools and notation can be used for analysis, design, and implementation modeling artifacts serve as documentation for the systems maintenance, and for refinement of the system as it is maintained Jonathan Sprinkle Object-Oriented Introduction 23

24 Development and Stages of Development Impact of models on development Since the generic concepts of identity, classification, inheritance, and polymorphism are applicable to the system model, as well as the implementation model, there is less entropy created during the transformation from design to implementation. This entropy is further reduced in the ability to prototype a system using these models during the analysis phase as well. Jonathan Sprinkle Object-Oriented Introduction 24

25 Development and Stages of Development OO Methodology Stages, per Rumbaugh 1 System conception 2 Analysis 3 Design 4 Implementation 5 (Maintenance/Testing) Jonathan Sprinkle Object-Oriented Introduction 25

26 Development and Stages of Development Analysis (in detail) 1 System conception: concept of application by users, managers, or professors 2 Analysis: Requirements gathered Concept refined What, not how, of the system, is extracted Model divided in two: Domain model (concepts and models for operation) Application model (concepts and models for user interaction) 3 Design 4 Implementation Jonathan Sprinkle Object-Oriented Introduction 26

27 Development and Stages of Development Design (in detail) 1 System conception: concept of application by users, managers, or professors 2 Analysis 3 Design: System Design Architecture established Programming language(s) and middleware chosen Policies clarified (especially testing!) Performance estimates established, and vetted (i.e., bounds established) Class Design Analysis models extended to incorporate system design Application and Domain models expanded, clarified Data structures established 4 Implementation Jonathan Sprinkle Object-Oriented Introduction 27

28 Development and Stages of Development Implementation (in detail) 1 System conception: concept of application by users, managers, or professors 2 Analysis 3 Design 4 Implementation: Class Designs mapped to language(s) Databases implemented Hardware stand-up Software Engineering practices must be used! Jonathan Sprinkle Object-Oriented Introduction 28

29 Development and Stages of Development Comments on Rumbaugh Development Process Note that this list is very representative, but the complexity of software means that the implementation may be drastically different on different projects. Policies which are established in the design phase may need to be drastically changed if requirements are gathered too late, or assumptions are proved unjustified Note that testing should be considered in all design phases!! Jonathan Sprinkle Object-Oriented Introduction 29

30 Outline 1 An Object Oriented Manifesto? What s in an Object? Object-Oriented Definitions 2 Object-Oriented Development Development and Stages of Development 3 Kinds of models Structural Modeling Behavioral Modeling Interaction Modeling 4 The Class Diagram In the beginning... Graphical Notations 5 Inheritance Notation 6 Association Graphical Notations Jonathan Sprinkle Object-Oriented Introduction 30

31 Structural Modeling Class Models Definition The class model describes the static structure of the objects in a system, and their relationships. This class model is composed of class diagrams. Definition A class diagram is a graph whose nodes are classes and whose arcs are the relationships among classes. Definition An object diagram is a graph whose nodes are class instances and whose arcs are the relationships among objects. Jonathan Sprinkle Object-Oriented Introduction 31

32 Behavioral Modeling State Models Definition The state model describes the aspects of an object that change over time. This state model is composed of state diagrams. Definition A state diagram is a graph whose nodes are states, and whose arcs are transitions between states caused by events. Jonathan Sprinkle Object-Oriented Introduction 32

33 Interaction Modeling Interaction Models Definition The interaction model describes how the objects in a system cooperate to achieve broader results. Interaction models are useful in the analysis phase, and project conception phase. Purposes of interaction models include flesh out, before code is written, the cases in which the system is expected to operate; explicate what interaction (if any) is done with a user (or between objects); and sketch behaviors of objects informally, to estimate complexity of implementation Jonathan Sprinkle Object-Oriented Introduction 33

34 Interaction Modeling Use Cases Definition A use case is an interaction model which focuses on the functionality of a systemnamely what the system does for users, and is most important in the analysis phase. Jonathan Sprinkle Object-Oriented Introduction 34

35 Interaction Modeling Sequence Diagrams Definition A sequence diagram shows the objects that interact and the time sequence of their interactions, and is most important in the design phase Jonathan Sprinkle Object-Oriented Introduction 35

36 Interaction Modeling Activity Diagrams Definition An activity diagram elaborates important processing steps, and is most important in the analysis phase Jonathan Sprinkle Object-Oriented Introduction 36

37 Outline 1 An Object Oriented Manifesto? What s in an Object? Object-Oriented Definitions 2 Object-Oriented Development Development and Stages of Development 3 Kinds of models Structural Modeling Behavioral Modeling Interaction Modeling 4 The Class Diagram In the beginning... Graphical Notations 5 Inheritance Notation 6 Association Graphical Notations Jonathan Sprinkle Object-Oriented Introduction 37

38 In the beginning... there was the cloud Operation 1 Operation 2... Attribute 1 Attribute 2... Class A Figure: Booch Forecast: Cloudy Jonathan Sprinkle Object-Oriented Introduction 38

39 In the beginning... Booch-yah! Figure: Grady Booch Grady Booch, one of the founders of UML, devised a notation that could represent abstract data types (i.e., classes) graphically. This idea, coupled with the OMT of Rumbaugh, and the other contributions of Ivar Jacobsen, later created UML. But, before we digress, what was the purpose of class diagrams? Jonathan Sprinkle Object-Oriented Introduction 39

40 In the beginning... Inspi(red) In the beginning, class diagrams were an inspiration and documentation feature. diagrams could be drawn when performing the domain model and application model analysis used to flesh out the various classes required once classes were written, the final code was supplemented with a diagram describing the relationships between classes Jonathan Sprinkle Object-Oriented Introduction 40

41 In the beginning... If you can t stand the heat... When UML came together there were heated arguments about what a class should look like. Should the boundaries of a class should be wavy, to symbolize how software is cloud-like (e.g., an idea), or should they be rigid to symbolize how the class actually is? Jonathan Sprinkle Object-Oriented Introduction 41

42 In the beginning in the end. Regardless of whose idea was best, the following was finally settled on: Class Name attr attr : DataType[attMult] attr : DataType[attMult] = defaultvalue operation operation : ResultType operation( arg1:name1,... ) : ResultType Figure: A basic UML class Jonathan Sprinkle Object-Oriented Introduction 42

43 Graphical Notations Relationships Given this basic graphical notation, it is possible to show the following kinds of relationships between classes: Inheritance Association Encapsulation Jonathan Sprinkle Object-Oriented Introduction 43

44 Graphical Notations Other uses In addition, it is possible to use class diagrams for Comments Cardinality/multiplicity denotation Package hierarchy Role-based associations Access region specification Constraints We will delve into much of these extra details in future classes. Jonathan Sprinkle Object-Oriented Introduction 44

45 Outline 1 An Object Oriented Manifesto? What s in an Object? Object-Oriented Definitions 2 Object-Oriented Development Development and Stages of Development 3 Kinds of models Structural Modeling Behavioral Modeling Interaction Modeling 4 The Class Diagram In the beginning... Graphical Notations 5 Inheritance Notation 6 Association Graphical Notations Jonathan Sprinkle Object-Oriented Introduction 45

46 Notation Superclass Subclass Figure: Inheritance Notation Inheritance is denoted using the open triangle. The triangle points to the superclass, and extends to the subclass(es). It is considered appropriate to have extensions from a single triangle to multiple subclasses, or to have one triangle for each subclass (tool-specific, or users choice). Generally, superclasses are above the subclass on the diagram, but this is not semantically enforced, and in many cases may decrease readability. Inheritance fulfills the IS-A definitions. IS-A implies generalization or specialization between the base and derived class. A derived class can be treated like a base class object under all circumstances. Jonathan Sprinkle Object-Oriented Introduction 46

47 Notation Example 24 Example A GraduateStudent IS-A Student Student credits : int GraduateStudent passedquals : bool degreesought : string Jonathan Sprinkle Object-Oriented Introduction 47

48 Notation Example 25 Example A Student IS-A Person Person lastname : string birthdate : date address : string Student credits : int Jonathan Sprinkle Object-Oriented Introduction 48

49 Notation Example 26 Example A Truck IS-A Automobile Automobile mass : double cylinders : int start( ) : bool getspeed( ) : double settireangle( double ) Truck bedsize : double thirddoor : bool getmaxtow( ) : double istowing( ) : bool Jonathan Sprinkle Object-Oriented Introduction 49

50 Outline 1 An Object Oriented Manifesto? What s in an Object? Object-Oriented Definitions 2 Object-Oriented Development Development and Stages of Development 3 Kinds of models Structural Modeling Behavioral Modeling Interaction Modeling 4 The Class Diagram In the beginning... Graphical Notations 5 Inheritance Notation 6 Association Graphical Notations Jonathan Sprinkle Object-Oriented Introduction 50

51 Graphical Notations What is an association, again? An association is a relationship between classes, which (at runtime) is called a link. An association may have a resulting role and multiplicity that gives further information regarding the relationship. Associations are shown by a line in the class diagram, with optional rolenames and multiplicities. Example Student with a GetsScholarship association with a Foundation Student credits : int GetsScholarship Company name : string address : string Jonathan Sprinkle Object-Oriented Introduction 51

52 Graphical Notations Example 28 Example Student SitsAt Desk (1,1) Student credits : int SitsAt 1 1 Seats Desk Read: Student SitsAt 1 Desk ; or Desk Seats 1 Student Note: when multiplicities are omitted, they default to 1. Jonathan Sprinkle Object-Oriented Introduction 52

53 Nonsymmetric Multiplicities Example 29 Example A Student can tutor another Student (1:tutor, 1..*:tutee) Student credits : int tutor tutee 1..* Here we see how a class can have an association with itself. Note that the Student playing the role of tutor may not be the same as playing the role of tutee. Jonathan Sprinkle Object-Oriented Introduction 53

54 Nonsymmetric Multiplicities Example 30 An association may also be specialized by a particular class. This association class may provide more attributes to describe the association. Example Person, as a supervisor, Manage employees (0 or more Person) Person lastname : string birthdate : date address : string supervisor 0..1 employee 0..* Manage performancerating : int Jonathan Sprinkle Object-Oriented Introduction 54

55 Nonsymmetric Multiplicities Example 31 Example Person lastname : string birthdate : date address : string * 0..1 Job title : str salary : int Company name : string address : string Note that * and 0..* are interchangeable. Also, while rolenames are useful, they are only really required if an association is for the same class at each end. Jonathan Sprinkle Object-Oriented Introduction 55

56 Nonsymmetric Multiplicities Next time: Encapsulation examples Advanced details of Class Diagrams Read the chapters in Rumbaugh on Class Diagrams, and advanced Class Diagrams Jonathan Sprinkle Object-Oriented Introduction 56