Creating Your Own Classes

Transcription

1 4 Creating Your Own Classes C# Programming: From Problem Analysis to Program Design C# Programming: From Problem Analysis to Program Design 1 4th Edition

2 Chapter Objectives C# Programming: From Problem Analysis to Program Design 2

3 The Object Concept 3

4 Example1 A Classical View of a Class Diagram PERSON Attributes - personname : string - personage : int This style is commonly used by Java and C++ developers. Constructor(s) + Person() + Person(string namevalue, int agevalue) Accessors / Mutators + GetPersonName() : string + SetPersonName(string namevalue) + GetPersonAge() : int + SetPersonAge(int agevalue) User-Defined Methods + ToString() : string other methods here

5 Example2 C# Class Diagrams: Geometric Figures

6 Example3 University Seminar - Class Diagram Note: This UML Class Diagram shows multiple cooperative classes as well as the associations (links) between them. 6

7 Example4 An Inventory System - Class Diagram 7

8 Example5 A Library System

9 Example6 Class Inheritance This diagram shows the super-class Person and two descendant classes Student and Faculty, that generalize the ancestor class. We will study Inheritance in chapter 11.

10 Writing Your Own Classes 10

11 Making a Class - Private Member Data 11

12 C# Implementation of Private Member Data (continued) public class Student { //Data members (data fields, or characteristics) private string studentnumber; } private string studentlastname; private string studentfirstname; private int score1; private int score2; private int score3; private string major;... All data member names should be entered using Camel-Notation. Their corresponding property names should use Pascal- Notation (later)

13 How to Create a Class using VS? DRAWING THE CLASS 13

14 Class Diagram Private member variables Open the Class Diagram from Solution Explorer (right-click) View Class Diagram Public Properties (accessors) User Defined Methods In VS2017 you need to install the graphic design tool. Go to menu Tools-> Get Tools and Features. Pick 'Visual Studio extension development' workload, choose 'Class Designer' option. Install. 14

15 Class Diagram (continued) Right click on class diagram to open Class Details window 15

16 Class Diagram (continued) When you complete 'drawing' the Student class using the Class Diagram tool, its corresponding code is automatically placed in the file Student.cs Figure 4-3 Skeleton of auto generated code made for the Student class diagram 16

17 Creating Objects from Classes Student s1 = new Student("1000", "Daenerys", "Targaryen", 99, 100, 100, "Political Sc."); Student s2 = new Student("1000", "Lannister", "Cersei", 50, 55, 65, "Social Services"); new null 17

18 Parts of a class: Constructors 18

19 Constructor (you need to type in this code) public //Default constructor - ZERO ARGUMENTS CONST. public Student() { studentnumber = " "; studentlastname = "n.a."; studentfirstname = "n.a."; score1 = 0; score2 = 0; score3 = 0; major = "Not declared yet"; } (must) //Constructor with six arguments - ALL AGRGUMENTS CONST. public Student(string numbervalue, string lastnamevalue, string firstnamevalue, int s1value, int s2value, int s3value, string majorvalue) { studentnumber = numbervalue; studentlastname = lastnamevalue; studentfirstname = firstnamevalue; score1 = s1value; score2 = s2value; score3 = s3value; major = majorvalue; } (must) 19

20 Constructor (continued) //Constructor with three parameters (optional) public Student (string idvalue, string firstvalue, string lastvalue) { studentnumber = idvalue; studentfirstname = firstvalue; studentlastname = lastvalue; } 20

21 Moving Data In/Out of Class Student Data Methods Value 21

22 Accessors Classic Style (Java, C++, etc.) public double GetStudentNumber( ) { return studentnumber; } Get Accessor Student Data Methods 22

23 Accessors Classic Style (Java, C++, etc.) public void SetScore1( int gradevalue) { if (gradevalue < 0) { //convert negative grades to zero gradevalue = 0; } score1 = gradevalue; } Student Data Methods value 23

24 Accessors Classic Style (Java, C++, etc.) public double SetNoOfSqYards(double squareyards) { noofsquareyards = squareyards; } Mutator public void SetNoOfSquareYards(double length, double width) { noofsquareyards = length * width; } Accessors could be overridden Overloaded 24

25 User-defined Methods public double CalculateAverage( ) { return (score1 + score2 + score3) / 3.0; } 25

26 Using C# Property 26

27 class Student { //private data members... private int score1;... C# Property //Properties public int Score1 { get { return score1; } set { //convert incoming negative grades to zero } } if (value < 0) { value = 0; } score1 = value; value is a special C# variable used as general alias for input data arriving to a property. } //...rest of the class goes here... 27

28 Property (continued) value s1 s1.score1 = 100; value Score1. 28

29 ToString( ) Method ToString() //show yourself! Equals() //are you equal to this other object? GetType() //tell what type of data item you are GetHashCode() //tell your unique identifier code ToString() ToString() Write() WriteLine() Console.WriteLine(s1); Console.WriteLine(s1.ToString()); 29

30 ToString( ) Method (continued) Returns a human-readable string Can write a new definition for the ToString() method to include useful details public override string ToString( ) { } // return string value Keyword override added to provide new implementation details It is understood that we must always override the ToString() method. This enables us to decide what should be displayed if the object is printed 30

31 Example - ToString( ) public override string ToString() { string niceoutput = "Student [" + " No: " + StudentNumber + " First: " + StudentFirstName + " Last: " + StudentLastName + " Score1: " + Score1 + " Score2: " + Score2 + " Score3: " + Score3 + " Major: " + Major + "]"; return niceoutput; } 31

32 Calling Instance Methods object.method(args) CalculateAverage() finalgrade = s1.calculateaverage(); Console answer = Math.Pow(4, 2); Console.WriteLine("hello"); Math ClassName.method(args) 32

33 Testing Your New Class A different class is needed for testing and using your class Test class has Main( ) in it Construct objects of your class Use the properties to assign and retrieve values Invoke instance methods using the objects you construct C# Programming: From Problem Analysis to Program Design 33

34 Calling the Constructor Method Figure 4-4 Intellisense displays available constructors C# Programming: From Problem Analysis to Program Design 34

35 Using Public Members Figure 4-5 Public members of the Student class 35

36 StudentApp Figure 4-6 Output from StudentApp Review StudentApp Project C# Programming: From Problem Analysis to Program Design 36

37 Test Class 37

38 Testing Your New Class Figure 4-7 Output from Carpet example using instance methods Review CarpetCalculator Project 38

39 Example - English Distance Class 39

40 Example - English Distance Class 1 of 4 class EDistance { //OK to make constant publicly available (prefix EDistance.) public const double INCHES_TO_CM = 2.54; //properties & private members private int feet; private int inches; public int Inches { get { return inches; } set { //correct inches in case they are > 12 feet += value / 12; inches = value % 12; } } 40

41 Example - English Distance Class 2 of 4 public int Feet { get { return feet; } set { feet = value; } } //constructor(s) public EDistance() { //Observe, we use properties, not the priv. vars. Feet = 0; Inches = 0; } public EDistance(int feetvalue, int inchesvalue) { //Style: add postfix Value to each incoming argument Feet = feetvalue; Inches = inchesvalue; } 41

42 Example - English Distance Class 3 of 4 //user-defined methods public override string ToString() { } return string.format("edistance [ {0}\' {1}\" ]", Feet, Inches); } } public double ToMeters() { double cm = (12 * Feet + Inches) * INCHES_TO_CM; return cm / 100; } 42

43 Example - English Distance Class 4 of 4 //Testing the EDistance class class Program { static void Main(string[] args) { //call the all-arguments constructor EDistance ed1 = new EDistance(6, 2); Console.WriteLine(ed1); Console.WriteLine(ed1.ToMeters()); } } //call the zero-arguments constructor EDistance ed2 = new EDistance(); ed2.feet = 3; ed2.inches = 14; Console.WriteLine(ed2); Console.Read(); 43

44 RealEstateInvestment Example Figure 4-8 Problem specification for RealEstateInvestment example 44

45 Data for the RealEstateInvestment Example Table 4-2 Instance variables for the RealEstateInvestment class 45

46 Data for the RealEstateInvestment Example (continued) Table 4-3 local variables for the property application class C# Programming: From Problem Analysis to Program Design 46

47 RealEstateInvestment Example (continued) Figure 4-9 Prototype C# Programming: From Problem Analysis to Program Design 47

48 RealEstateInvestment Example (continued) Figure 4-10 Class diagrams C# Programming: From Problem Analysis to Program Design 48

49 RealEstateInvestment Example (continued) Table 4-4 Properties for the RealEstateInvestment class C# Programming: From Problem Analysis to Program Design 49

50 RealEstateInvestment Example (continued) Figure 4-11 Structured English for the RealEstateInvestment example C# Programming: From Problem Analysis to Program Design 50

51 Class Diagram Figure 4-12 RealEstateInvestment class diagram C# Programming: From Problem Analysis to Program Design 51

52 Test and Debug Figure 4-13 Output from RealEstate Investment example View RealEstateInvestment C# Programming: From Problem Analysis to Program Design 52

53 Coding Standards Naming Conventions Classes Properties Methods Constructor Guidelines Spacing Guidelines C# Programming: From Problem Analysis to Program Design 53

54 Resources C# Programming: From Problem Analysis to Program Design 54

55 Chapter Summary Components of a method: modifiers + returntype + methodname + parameters + body Class methods Parameters: value, ref, out, default values Predefined methods (ToString, Equals, ) Value- and nonvalue-returning methods C# Programming: From Problem Analysis to Program Design 55

56 Chapter Summary (continued) Properties Instance methods Constructors Mutators / Accessors User-defined methods Types of parameters C# Programming: From Problem Analysis to Program Design 56