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繼承 (Inheritance)

繼承 (Inheritance). 鄭士康 國立台灣大學 電機工程學系 / 電信工程研究所 / 資訊網路與多媒體研究所. UsingInheritance.Program (1/7). using System; namespace UsingInheritance { /* * 示範繼承的使用 * 4/23/2007 */ class Program { static void Main(string[] args) {

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繼承 (Inheritance)

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  1. 繼承(Inheritance) 鄭士康 國立台灣大學 電機工程學系/電信工程研究所/ 資訊網路與多媒體研究所

  2. UsingInheritance.Program (1/7) using System; namespace UsingInheritance { /* * 示範繼承的使用 * 4/23/2007 */ class Program { static void Main(string[] args) { AdvancedCalculator calculator = new AdvancedCalculator();

  3. UsingInheritance.Program (2/7) int op = 0; int operand1 = 0; int operand2 = 0; int result; double angle = 0.0; double functionValue; do { Console.Write( "指定運算: 0. 結束; 1. 加; 2. 減; 3. 乘; 4. 除; " +" \n 5. 正弦函數; 6. 餘弦函數; 7. 正切函數: "); op = int.Parse(Console.ReadLine()); if (op == 0) break; if (op > 7) continue;

  4. UsingInheritance.Program (3/7) if (op < 5) { Console.Write("輸入第一個數字: "); operand1 = int.Parse(Console.ReadLine()); Console.Write("輸入第二個數字: "); operand2 = int.Parse(Console.ReadLine()); } else { Console.Write("輸入角度(度)"); angle = double.Parse(Console.ReadLine()); } switch (op) {

  5. UsingInheritance.Program (4/7) case 1: result = calculator.Add(operand1, operand2); Console.WriteLine("{0} + {1} = {2} ", operand1, operand2, result); break; case 2: result = calculator.Subtract(operand1, operand2); Console.WriteLine("{0} - {1} = {2} ", operand1, operand2, result); break; case 3: result = calculator.Multiply(operand1, operand2);

  6. UsingInheritance.Program (5/7) Console.WriteLine("{0} * {1} = {2} ", operand1, operand2, result); break; case 4: result = calculator.Divide(operand1, operand2); Console.WriteLine("{0} / {1} = {2} ", operand1, operand2, result); break; case 5: functionValue = calculator.getSine(angle); Console.WriteLine( "Sine of {0} (deg) = {1}", angle, functionValue); break;

  7. UsingInheritance.Program (6/7) case 6: functionValue = calculator.getCosine(angle); Console.WriteLine( "Cosine of {0} (deg) = {1}", angle, functionValue); break; case 7: functionValue = calculator.getTangent(angle); Console.WriteLine( "Tangent of {0} (deg) = {1}", angle, functionValue); break;

  8. UsingInheritance.Program (7/7) default: Console.WriteLine( "Should not see this message. Debug!!!"); break; } } while (true); } } }

  9. UsingInheritance.AdvancedCalculator (1/2) using System; namespace UsingInheritance { /* * 可計算三角函數之計算器 * 4/23/2007 */ public class AdvancedCalculator : Calculator { public double getSine( double angle ) { angle *= Math.PI/180.0; return Math.Sin(angle); }

  10. UsingInheritance.AdvancedCalculator (2/2) public double getCosine( double angle ) { angle *= Math.PI/180.0; return Math.Cos(angle); } public double getTangent( double angle ) { angle *= Math.PI/180.0; return Math.Tan(angle); } } }

  11. UsingInheritance.Calculator (1/2) using System; namespace UsingInheritance { /* * 計算器 * 3/17/2007 */ class Calculator { public int Add(int a, int b) { int result = a + b; return result; }

  12. UsingInheritance.Calculator (2/2) public int Subtract(int a, int b){ int result = a - b; return result; } public int Multiply(int a, int b){ int result = a * b; return result; } public int Divide(int a, int b){ int result = a / b; return result; } } }

  13. 表示繼承的UML類別圖 Calculator Add() Subtraction() Multiply() Divide() AdvancedCalculator getSine() getCosine() getTangent()

  14. A B C 類別繼承之階層關係 class A { public int data1; public int data2; //…other members are methods }; class B : public A { public int data3; //…other members are methods }; class C : public B { public int data1; public int data4; //…other members are methods };

  15. data1 data2 data1 data2 data3 物件記憶體分配模型 A a; B b; C c; a c A.data1 data2 data3 data1 b data4

  16. UsingProtected.Program (1/2) using System; namespace UsingProtected { /* 示範protected成員之使用 * 4/23/2007 */ class Program { static void Main(string[] args) { DC d = new DC(); d.setX(3); //Console.WriteLine( d.getX() ) ; // Error! // d.x = 77; // Error! d.add2(); } }

  17. UsingProtected.Program (2/2) public class BC { public void setX( int x ) { this.x = x; } protected int getX() { return x; } private int x; } public class DC : BC { public void add2() { int c = getX(); setX( c+2 ); } } }

  18. 限制繼承 sealed class SClass { . . . . . . }

  19. 物件導向的關鍵技術 • 封裝(packaging) • 繼承(inheritance) • 多型(polymorphism)

  20. 多型 • 編譯時連結(compile-time binding)與執行時連結(run-time binding) • 靜態連結(static binding)與動態連結(dynamic binding) • 多型之要求 • 繼承階層體系 • 虛擬(virtual)與覆寫(override) • 基礎類別之參考 • 多型之優缺點

  21. UsingOverride.Program (1/3) using System; namespace UsingOverride { /* 示範方法函式之覆寫(overriding)與多型 * 5/2/2007 */ class Program { static void Main(string[] args) { Console.WriteLine( "選擇列印尺寸規格: 1. B4 ; 2. A3 ; 其他: 標準(A4)");

  22. UsingOverride.Program (2/3) int reportType = int.Parse(Console.ReadLine()); Console.WriteLine(); Printer pr; switch (reportType) { case 1: pr = new PrinterB4(); pr.Print(); break; case 2: pr = new PrinterA3(); pr.Print(); break; default: pr = new Printer(); pr.Print(); break; }

  23. UsingOverride.Program (3/3) Console.WriteLine(); Console.ReadLine(); }

  24. UsingOverride.Printer (1/2) using System; namespace UsingOverride { /* * 模擬標準印表機 * 5/1/2007 */ class Printer { public Printer() { Console.WriteLine("印表機備便"); } virtual public void Print() { Console.WriteLine("列印標準尺寸"); Finish("標準"); } Printer Print()

  25. UsingOverride.Printer (2/2) protected void Finish(string type) { Console.WriteLine("{0}報表列印完成", type); } } }

  26. UsingOverride. PrinterB4 using System; namespace UsingOverride{ /* * 模擬B4印表程式 * 5/1/2007 */ class PrinterB4 : Printer{ public PrinterB4(){ Console.WriteLine("B4尺寸列印程式備便"); } override public void Print(){ Console.WriteLine("列印B4尺寸"); Finish("B4"); } } }

  27. UsingOverride. PrinterA3 using System; namespace UsingOverride{ /* * 模擬A3印表程式 * 5/1/2007 */ class PrinterA3 : Printer{ public PrinterA3(){ Console.WriteLine("A3尺寸列印程式備便"); } override public void Print(){ Console.WriteLine("列印A3尺寸"); Finish("A3"); } } }

  28. 練習 • 撰寫類別Shape，定義虛擬方法Draw為輸出”畫形狀”字樣。其次撰寫類別Rectangle及Circle，分別覆寫Draw為輸出字串”畫長方形”及”畫圓形” 。寫一程式測試此一繼承結構之多型機制。

  29. UsingBase.Program (1/6) using System; namespace UsingBase { /* 示範base與new關鍵字的用法 * Ref: C# 程式設計人員參考 * 瞭解使用Override 和New 關鍵字的時機(C# 程式設計手冊) * ms-help://MS.VSExpressCC.v80/MS.NETFramework.v20.cht/dv_csref/html/323db184-b136-46fc-8839-007886e7e8b0.htm * 5/2/2007 */ class Program { static void Main(string[] args) {

  30. UsingBase.Program (2/6) // new and override make no differences here Car car1 = new Car(); car1.DescribeCar(); System.Console.WriteLine("----------"); ConvertibleCar car2 = new ConvertibleCar(); car2.DescribeCar(); System.Console.WriteLine("----------"); Minivan car3 = new Minivan(); car3.DescribeCar(); System.Console.WriteLine("----------");

  31. UsingBase.Program (3/6) // they are different in polymorphysm Car[] cars = new Car[3]; cars[0] = new Car(); cars[1] = new ConvertibleCar(); cars[2] = new Minivan(); foreach (Car vehicle in cars) { System.Console.WriteLine("Car object: " + vehicle.GetType()); vehicle.DescribeCar(); System.Console.WriteLine("----------"); } } }

  32. UsingBase.Program (4/6) // Define the base class class Car { public virtual void DescribeCar() { System.Console.WriteLine( "Four wheels and an engine."); } }

  33. UsingBase.Program (5/6) // Define the derived classes class ConvertibleCar : Car { public new virtual void DescribeCar() { base.DescribeCar(); System.Console.WriteLine( "A roof that opens up."); } }

  34. UsingBase.Program (6/6) class Minivan : Car { public override void DescribeCar() { base.DescribeCar(); System.Console.WriteLine( "Carries seven people."); } } }

  35. 覆寫與隱藏 • 覆寫: override • 主要用於Polymorphism (多型) • 執行時連結 • 隱藏: new • 只是取代基底類別同名之成員變數與方法 • 仍是編譯時連結

  36. UsingConstructorsForInheritance.Program (1/4) using System; namespace UsingConstructorsForInheritance{ /* * 示範繼承架構中的建構式呼叫 * 5/2/2007 */ class Program{ static void Main(string[] args){ Animal slug = new Animal(); Animal tweety = new Animal( "canary" ); Primate godzilla = new Primate(); Primate human = new Primate( 4 ); Human jill = new Human(); Console.ReadLine(); } }

  37. UsingConstructorsForInheritance.Program (2/4) class Animal { public Animal() { Console.WriteLine("Animal()"); species = "Animal"; } public Animal( string s ) { Console.WriteLine("Animal("+ s +")"); species = s; } private string species; }

  38. UsingConstructorsForInheritance.Program (3/4) class Primate : Animal { public Primate() : base() { Console.WriteLine( "Primate()" ); } public Primate( int n ) : base( "Primate" ) { Console.WriteLine("Primate(" + n +")"); heartCham = n; } private int heartCham; }

  39. UsingConstructorsForInheritance.Program (4/4) class Human : Primate { public Human() : base( 4 ) { Console.WriteLine( "Human()" ); } } }

  40. 預設類別System.Object • 一致化型別 • 成員函式 • Equals • GetHashCode • GetType • ReferenceEquals • ToString • Finalize

  41. InheritingObject.Program (1/2) using System; namespace InheritingObject{ /* * 示範Object類別 * 5/2/2007 */ class Program{ static void Main(string[] args){ Test t1 = new Test(); Test t2 = new Test(); bool isEqual = t1.Equals(t2); Console.WriteLine(t1.ToString()); Console.WriteLine("t1 與t2 相等為" + isEqual); Console.ReadLine(); } }

  42. InheritingObject.Program (2/2) class Test { override public string ToString() { return "覆寫InheritingObject.Test"; } } }

  43. Boxing 與 Unboxing int x = 10; Object obj = (Object) x; // boxing obj = 20; int j = (int)obj; // unboxing

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