繼承與多型 (Inheritance and Polymorphism)

繼承與多型 (Inheritance and Polymorphism)
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

綱要繼承修飾語protected 限制繼承繼承架構下的建構函式呼叫 OCP:開放-封閉原理多型二十一點模擬程式0.1版
*覆寫與隱藏

綱要預設類別System.Object LSP: Liskov替代性原理抽象類別 DIP: 依存性反轉原理介面 ISP: 介面分離原理
多重介面 *多重介面鑄形

綱要繼承修飾語protected 限制繼承繼承架構下的建構函式呼叫 OCP:開放-封閉原理多型二十一點模擬程式0.1版覆寫與隱藏

UsingInheritance.Calculator 片段
public int Add(int a, int b) { int result = a + b; return result; } public int Subtract(int a, int b) { int result = a - b; public int Multiply(int a, int b) int result = a * b;

UsingInheritance.Program. Program.Main() 片段(1/2)
AdvancedCalculator calculator = new AdvancedCalculator(); . . . switch (op) { case 1: result = calculator.Add(operand1,operand2); Console.WriteLine("{0} + {1} = {2} ", operand1, operand2, result); break;

UsingInheritance.Program. Program.Main() 片段(2/2)
case 5: functionValue = calculator.GetSine(angle); Console.WriteLine( "Sine of {0} (deg) = {1}", angle, functionValue); break; . . . }

UsingInheritance.AdvancedCalculator 片段
public class AdvancedCalculator : Calculator { public double GetSine(double angle) angle *= Math.PI / 180.0; return Math.Sin(angle); } . . .

表示繼承的UML類別圖

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

物件記憶體分配模型 A a = new A(); data1 a B b = new B(); C c = new C(); data2 c

練習實作並測試下列繼承關係

UsingProtected.Program. Program.Main()片段
DC d = new DC(); d.SetX(3); //Console.WriteLine( d.GetX() ) ; // Error! //d.x = 77; // Error! d.Add2();

UsingProtected.Program片段
class BC { private int x; public void SetX( int x ) { this.x = x; } protected int GetX() { return x; } } class DC : BC public void Add2() int c = GetX(); SetX( c+2 );

限制繼承 sealed class SClass { }

UsingConstructorsForInheritance. Program.Main() 片段
Animal slug = new Animal(); Animal tweety = new Animal( "canary" ); Primate godzilla = new Primate(); Primate human = new Primate( 4 ); Human jill = new Human();

UsingConstructorsForInheritance.Program 片段(1/3)
class Animal { private string species; public Animal() Console.WriteLine("Animal()"); species = "Animal"; } public Animal( string s ) Console.WriteLine("Animal("+ s +")"); species = s;

class Primate : Animal { private int heartCham; public Primate() : base() Console.WriteLine( "Primate()" ); } public Primate( int n ) : base( "Primate" ) Console.WriteLine("Primate(" + n +")"); heartCham = n;

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

衍生物件產生流程 Primate human = new Primate( 4 );
public Primate( int n ) : base( "Primate" ) { . . . } public Animal( string s ) { . . . }

練習利用偵錯器體驗了解程式UsingConstructorsForInheritance

開放-封閉原理 (OCP:Open-Closed Principle)
Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification 增添軟體單元新功能，但不影響此軟體單元的程式碼 *Robert C. Martin, Agile Software Development: Principles, Patterns, and Practices, Pearson Education, 2003

程式OCPViolationExample類別圖

OCPViolationExample.Program. Program.Main() 片段
Point center; center.x = 15; center.y = 20; Point topLeft; topLeft.x = 30; topLeft.y = 40; Shape[] list = { new Circle(2, center), new Rectangle(3, 4, topLeft) }; DrawAllShapes(list);

OCPViolationExample.Program.Program 片段 (1/2)
static void DrawAllShapes(Shape[] list) { for (int i = 0; i < list.Length; ++i) { Shape s = list[i]; switch (s.type) { case ShapeType.CIRCLE: DrawCircle((Circle) s); break; case ShapeType.RECTANGLE: DrawRectangle((Rectangle) s); }

OCPViolationExample.Program.Program 片段 (2/2)
static void DrawCircle(Circle c) { Console.WriteLine("Draw a circle"); } static void DrawRectangle(Rectangle r) Console.WriteLine("Draw a rectangle");

OCPViolationExample.Program 片段 (1/2)
class Shape { public ShapeType type; public Shape(ShapeType t) { type = t; } class Circle : Shape { private int radius; private Point center; public Circle(int radius, Point center) :base(ShapeType.CIRCLE) { this.radius = radius; this.center = center;

OCPViolationExample.Program 片段 (2/2)
class Rectangle : Shape { private int width; private int height; private Point topLeft; public Rectangle(int width, int height, Point topLeft) : base(ShapeType.RECTANGLE) this.width = width; this.height = height; this.topLeft = topLeft; }

OCPViolationExample的主要問題
添加任何有關Shape的演算(例如，拖曳、伸縮、移動、刪除)都要重複麻煩的switch敘述增加一種新的Shape子類別，必須修改enum敘述、各處的switch敘述，並在類別Program增加對應的Draw函式

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

多型編譯時連結(compile-time binding)與執行時連結(run-time binding) 多型之要求多型之優缺點
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

DrawingAllShapes類別圖

DrawingAllShapes.Program. Program.Main() 片段(1/2)
Shape[] list = new Shape[2]; Point center; center.x = 15; center.y = 20; Point topLeft; topLeft.x = 30; topLeft.y = 40; Circle c = new Circle(2, center); Rectangle r = new Rectangle(3, 4, topLeft); Console.WriteLine("決定畫圖順序, 輸入"); Console.WriteLine("1: 圓形, 矩形"); Console.WriteLine("2: 矩形, 圓形"); int ans = int.Parse(Console.ReadLine());

DrawingAllShapes.Program. Program.Main() 片段(2/2)
switch (ans) { case 1: list[0] = c; list[1] = r; break; case 2: list[0] = r; list[1] = c; default: . . . } DrawAllShapes(list);

DrawingAllShapes.Program. Program 片段
static void DrawAllShapes(Shape[] list) { int i; for (i = 0; i < list.Length; ++i) list[i].Draw(); }

DrawingAllShapes.Program 片段(1/3)
class Shape { public Shape() { } virtual public void Draw() { } }

class Circle : Shape { private int radius; private Point center; public Circle(int radius, Point center) this.radius = radius; this.center = center; } override public void Draw() Console.WriteLine("Draw a circle");

class Rectangle : Shape { private int width; private int height; private Point topLeft; public Rectangle(int width, int height, Point topLeft) { this.width = width; this.height = height; this.topLeft = topLeft; } override public void Draw() { Console.WriteLine("Draw a rectangle");

練習在程式DrawingAllShapes增加類別Triangle，使程式也能畫出三角形。

BlackJack_0_1 類別圖

BlackJack_0_1.BlackJackTest 片段(1/2)
public static bool Scenario1_OK() { Card[] cards = { new Card(Suit.SPADE, 1), new Card(Suit.HEART, 11), new Card(Suit.DIAMOND, 10) }; Deck deck = new Deck(cards); Player player = new Player(); Dealer dealer = new Dealer();

BlackJack_0_1.BlackJackTest 片段(2/2)
player.SaveACard(deck.DealACard()); dealer.SaveACard(deck.DealACard()); return( player.GetStatus() == Status.BLACK_JACK && dealer.GetStatus() == Status.PASS); }

BlackJack_0_1.Game 片段 (1/6)
const int N_PLAYERS = 2; Deck deck; Player[] players = new Player[N_PLAYERS]; public Game() { players[0] = new Player("Jeng"); players[N_PLAYERS-1] = new Dealer(); }

private void Play() { int i; // 第一輪發牌 for (i = 0; i < N_PLAYERS; ++i) players[i].SaveACard( deck.DealACard()); players[i].Dump(); }

// 第二輪發牌 for (i=0; i < N_PLAYERS; ++i) { players[i].SaveACard( deck.DealACard()); players[i].Dump(); }

// 開始要牌計牌 for(i=0; i<N_PLAYERS; ++i) { while (players[i].GetStatus() == Status.PASS && players[i].WantOneMoreCard() && deck.HasMoreCard()) players[i].SaveACard(deck.DealACard()); players[i].Dump(); if(IsBlackJackOrBurst(players[i])) return; }

// 計點分勝負 Player dealer = players[N_PLAYERS-1]; for(i=0; i<N_PLAYERS-1; ++i) { if (dealer.GetTotalPoints() >= players[i].GetTotalPoints()) { Console.WriteLine( dealer.Name + "勝"+players[i].Name); } else { Console.WriteLine( players[i].Name+"勝"+dealer.Name); }

private bool IsBlackJackOrBurst( Player player) { bool isBlackJack = false; if (player.GetStatus()==Status.BLACK_JACK) { isBlackJack = true; Console.WriteLine(player.Name+ " BlackJack!!!"); } bool isBurst = false; if (player.GetStatus() == Status.BURST){ isBurst = true; Console.WriteLine(player.Name+" 爆!!!"); return (isBlackJack || isBurst);

BlackJack_0_1.Player 片段(1/5)
private Card[] hand = new Card[11]; private int nCards; private Status status; private int totalPoints; private string name; public Player() { nCards = 0; name = "無名氏"; }

public Player(string name) { nCards = 0; this.name = name; } public string Name get { return name; }

virtual public bool WantOneMoreCard() { Console.Write("要再一張牌嗎? (y/n) "); string answer = Console.ReadLine(); return (answer == "Y" || answer == "y"); }

public void Dump() { int i; Console.Write(name+" 牌: "); for (i = 0; i < nCards; ++i) hand[i].Dump(); Console.Write("\t"); if ((i + 1) % 5 == 0) Console.WriteLine(); }

Console.WriteLine(); Console.WriteLine(name + " 總點數: " + totalPoints); }

BlackJack_0_1.Dealer片段 class Dealer : Player {
public Dealer() : base("莊家") {} override public bool WantOneMoreCard() { return (base.GetTotalPoints() < 17); }

UsingBase.Program類別圖

UsingBase.Program片段 (1/3)
// Define the base class class Car { public virtual void DescribeCar() System.Console.WriteLine( "Four wheels and an engine."); }

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

class Minivan : Car { public override void DescribeCar() base.DescribeCar(); Console.WriteLine( "Carries seven people."); }

UsingBase.Program. Program.Main()片段 (1/2)
// new and override make no differences here Car car1 = new Car(); car1.DescribeCar(); Console.WriteLine(" "); ConvertibleCar car2 = new ConvertibleCar(); car2.DescribeCar(); Minivan car3 = new Minivan(); car3.DescribeCar();

UsingBase.Program. Program.Main()片段 (2/2)
// 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) { Console.WriteLine("Car object: " + vehicle.GetType()); vehicle.DescribeCar(); Console.WriteLine(" "); }

覆寫與隱藏覆寫: override 隱藏: new 主要用於Polymorphism (多型) 執行時連結
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

練習利用偵錯器體驗了解程式UsingBase

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

InheritingObject.Program. Program.Main()片段
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);

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

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

Liskov 代替性原理 (LSP: Liskov Substitution Principle)
Subtype must be substitutable for their base types 良好的繼承設計對形態S之每一物件o1，有形態T的物件o2，使在所有利用型態T物件的程式P中，P的行為不因以o1代替o2而改變破壞LSP常也破壞OCP *Robert C. Martin, Agile Software Development: Principles, Patterns, and Practices, Pearson Education, 2003

IS-A 關係與繼承

LSPViolationExample.Program 片段 (1/4)
class Rectangle { private int width; private int height; virtual public int Width set { width = value; } } virtual public int Height set { height = value; }

public int Area() { return width * height; }

class Square : Rectangle { override public int Width set { base.Width = value; base.Height = value; } } override public int Height

class Program { static void Main(string[] args) Square s = new Square(); Test(s); } static void Test(Rectangle r) r.Width = 5; r.Height = 4; Debug.Assert(r.Area() == 20);

函式的進入與離開條件進入與離開函式時的假設 Rectangle.Width的離開條件符合LSP之子類別函式覆寫的要求
Debug.Assert( (width == value) && (height == old.height)); 符合LSP之子類別函式覆寫的要求進入條件需等於父類別被覆寫函式之進入條件，或更寬鬆離開條件需等於父類別被覆寫函式之離開條件，或更嚴格

抽象類別

AbstractClassExample.Program. Program.Main() 片段
double a = 5.0; Square sq = new Square(a); Console.WriteLine("正方形sq之面積為" + sq.Area()); Circle c = new Circle(a); Console.WriteLine("圓形c之面積為" + c.Area());

AbstractClassExample.Program 片段 (1/3)
public abstract class Shape { private string shape; public Shape(string shape) { this.shape = shape; Console.WriteLine("建立" + shape); } abstract public double Area();

public class Square : Shape { double a; public Square(double a): base("正方形") this.a = a; } public override double Area() return a * a;

public class Circle : Shape { double r; public Circle(double r): base("圓形") this.r = r; } public override double Area() return Math.PI * r * r;

練習將程式DrawingAllShapes中的類別Shape改為抽象類別，並將Shape.Draw()改為抽象函式

抽象類別修飾語欄位變數建構式函式方法覆寫與實作

依存性反轉原理 (DIP: Dependency-Inversion Principle)
High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions. *Robert C. Martin, Agile Software Development: Principles, Patterns, and Practices, Pearson Education, 2003

一個違反DIP的例子

狀態圖(State Chart)

DIPViolationExample.Program 片段 (1/4)
public enum LampStatus { OFF = 0, ON = 1 } public enum ButtonStatus RELEASED = 0, PRESSED = 1

public class Lamp { private LampStatus status = LampStatus.OFF; public LampStatus Status { get { return status; } } public void TurnOn() { status = LampStatus.ON; public void TurnOff() { status = LampStatus.OFF;

public class Button { private ButtonStatus status = ButtonStatus.RELEASED; private Lamp lamp; public Button(Lamp lamp) this.lamp = lamp; } public ButtonStatus Status { get { return status; }

public void Press() { if (status == ButtonStatus.RELEASED) { status = ButtonStatus.PRESSED; lamp.TurnOn(); } public void Release() { if( status == ButtonStatus.PRESSED ){ status = ButtonStatus.RELEASED; lamp.TurnOff();

DIPViolationExample.Program. Program.Main() 片段 (1/3)
Lamp lamp1 = new Lamp(1); Button button = new Button(lamp1); Random rand = new Random(); for (int n = 0; n <= 100; ++n) { Console.Write("time n = " + n + "\t");

if (rand.Next() % 2 == 1) { if (button.Status == ButtonStatus.PRESSED) button.Release(); } else button.Press();

if (lamp1.Status == LampStatus.OFF) { Console.WriteLine("lamp1 is off"); } else Console.WriteLine("lamp1 is on"); Console.WriteLine();

介面

UsingInterface.Program. Program.Main() 片段
double a = 5.0; Square sq = new Square(a); Console.WriteLine("正方形sq之面積為" + sq.Area()); Circle c = new Circle(a); Console.WriteLine("圓形c之面積為" + c.Area());

UsingInterface.Program片段(1/3)
interface Shape { double Area(); }

public class Square : Shape { double a; public Square(double a) this.a = a; } public double Area() return a * a;

public class Circle : Shape { double r; public Circle(double r) this.r = r; } public double Area() return Math.PI * r * r;

介面 vs. 抽象類別 (1/2) interface Shape { double Area(); }
public abstract class Shape { private string shape; public Shape(string shape) { this.shape = shape; Console.WriteLine("建立" + shape); abstract public double Area();

介面 vs. 抽象類別 (2/2) public class Square : Shape { . . .
public double Area() { return a * a; } public override double Area() {

一個符合DIP的設計

ButtonAndLamp.Program (1/4)
public interface SwitchableDevice { void TurnOn(); void TurnOff(); } public enum LampStatus { OFF = 0, ON = 1 public enum ButtonStatus { RELEASED = 0, PRESSED = 1

public class Lamp : SwitchableDevice { private LampStatus status = LampStatus.OFF; public LampStatus Status { get { return status; } } public void TurnOn() { status = LampStatus.ON; public void TurnOff() { status = LampStatus.OFF;

public class Button { private ButtonStatus status = ButtonStatus.RELEASED; private SwitchableDevice device; public Button(SwitchableDevice device) this.device = device; } public ButtonStatus Status { get { return status; }

public void Press() { if (status == ButtonStatus.RELEASED) { status = ButtonStatus.PRESSED; device.TurnOn(); } public void Release() { if (status == ButtonStatus.PRESSED) { status = ButtonStatus.RELEASED; device.TurnOff();

練習在程式ButtonAndLamp增加類別Fan，使Button也可以控制Fan的開與關

介面分離原理 (ISP: Interface-Segregation Principle)
Clients should not be forced to depend on methods that they do not use 避免同一介面中有目的不同的多群函式宣告

一個違反ISP的例子

ISPViolationExample.Program 片段 (1/4)
interface TimerClient { void TimeOut(); } interface Door : TimerClient { void Lock(); void Unlock(); bool IsOpen(); enum DoorStatus { CLOSED = 0, OPEN = 1

class Timer { private int t; private int timeout; private TimerClient client; public Timer(int timeout, TimerClient client) this.timeout = timeout; this.client = client; t = 0; }

public void Advance() { ++t; if (t % timeout == 0) { client.TimeOut(); } class TimedDoor : Door { private DoorStatus status = DoorStatus.CLOSED;

public bool IsOpen() { return (status == DoorStatus.OPEN); } public void Lock() { if (IsOpen()) status = DoorStatus.CLOSED; public void Unlock() { if (!IsOpen()) status = DoorStatus.OPEN; public void TimeOut() { Lock();

ISPViolationExample.Program. Program.Main() 片段(1/2)
TimedDoor tDoor = new TimedDoor(); int timeout = 10; Timer timer = new Timer(timeout, tDoor); int n; const int N = 20; tDoor.Unlock(); for (n = 0; n <= N; ++n) {

ISPViolationExample.Program. Program.Main() 片段(2/2)
if (tDoor.IsOpen()) { Console.WriteLine( "n = " + n + "\t tDoor is open"); } else "n = " + n + "\t tDoor is closed"); timer.Advance();

程式MultiInterface類別圖

MultiInterface.Program. Program.Main()片段
Floatplane fp = new Floatplane(); fp.Sail(); fp.Fly();

MultiInterface.Program片段 (1/2)
interface Plane { void Fly(); } interface Ship void Sail();

MultiInterface.Program片段 (2/2)
public class Floatplane : Plane, Ship { public Floatplane() { Console.WriteLine("建立水上飛機"); } public void Sail() { Console.WriteLine("水上滑行"); public void Fly() { Console.WriteLine("空中飛行");

練習利用多重介面，設計並測試一個類別Clock_Radio，兼具介面Clock之GetTime()與介面Radio之PlayMusic()功能

一個符合ISP的設計

TimedDoorSimulation.Program 片段
interface TimerClient { void TimeOut(); } interface Door { void Lock(); void Unlock(); bool IsOpen(); . . . class TimedDoor : Door, TimerClient {

程式CastMultiInterfaces類別圖

CastMultiInterfaces.Program. Program.Main()片段
double a = 5.0; Square sq = new Square(a); Rhombus rhomb = sq as Rhombus; Console.WriteLine( "sq的面積以菱形公式計算得"+rhomb.Area() ); if( sq is Rectangle ) { Rectangle rec = (Rectangle) sq; "sq的面積以矩形公式計算得"+rec.Area() ); }

CastMultiInterfaces.Program 片段(1/3)
interface Rectangle { double Area(); } interface Rhombus

public class Square : Rectangle, Rhombus { private double a; private double d; public Square(double a) this.a = a; d = Math.Sqrt(2.0) * a; }

double Rectangle.Area() { return a * a; } double Rhombus.Area() return 0.5 * d * d;

繼承與多型 (Inheritance and Polymorphism)

Similar presentations

Presentation on theme: "繼承與多型 (Inheritance and Polymorphism)"— Presentation transcript:

Similar presentations

About project

反馈

请登录

Auth with social network:

繼承與多型 (Inheritance and Polymorphism)

Similar presentations

Presentation on theme: "繼承與多型 (Inheritance and Polymorphism)"— Presentation transcript:

Similar presentations

About project

反馈