chap11.lst

Csharp2完全参考手册源代码 详细的说明可以在书里看到 该书是08年刚出炉很新鲜

// This program will not compile. 
 
class X { 
  int a; 
 
  public X(int i) { a = i; } 
} 
 
class Y { 
  int a; 
 
  public Y(int i) { a = i; } 
} 
 
class IncompatibleRef { 
  public static void Main() { 
    X x = new X(10); 
    X x2;  
    Y y = new Y(5); 
 
    x2 = x; // OK, both of same type 
 
    x2 = y; // Error, not of same type 
  } 
}

listing 14
// A base class reference can refer to a derived class object. 
 
using System; 
 
class X { 
  public int a; 
 
  public X(int i) { 
    a = i; 
  } 
} 
 
class Y : X { 
  public int b; 
 
  public Y(int i, int j) : base(j) { 
    b = i; 
  } 
} 
 
class BaseRef { 
  public static void Main() { 
    X x = new X(10); 
    X x2;  
    Y y = new Y(5, 6); 
 
    x2 = x; // OK, both of same type 
    Console.WriteLine("x2.a: " + x2.a); 
 
    x2 = y; // Ok because Y is derived from X 
    Console.WriteLine("x2.a: " + x2.a); 
 
    // X references know only about X members 
    x2.a = 19; // OK 
//    x2.b = 27; // Error, X doesn't have a b member 
  } 
}

listing 15
// Pass a derived class reference to a base class reference. 
 
using System; 
 
class TwoDShape { 
  double pri_width;  // private 
  double pri_height; // private 
 
  // Default constructor. 
  public TwoDShape() { 
    width = height = 0.0; 
  } 
 
  // Constructor for TwoDShape. 
  public TwoDShape(double w, double h) { 
    width = w; 
    height = h; 
  } 
 
  // Construct object with equal width and height. 
  public TwoDShape(double x) { 
    width = height = x; 
  } 
 
  // Construct object from an object. 
  public TwoDShape(TwoDShape ob) { 
    width = ob.width; 
    height = ob.height; 
  } 
 
  // Properties for width and height. 
  public double width { 
     get { return pri_width; } 
     set { pri_width = value; } 
  } 
 
  public double height { 
     get { return pri_height; } 
     set { pri_height = value; } 
  } 
 
  public void showDim() { 
    Console.WriteLine("Width and height are " + 
                       width + " and " + height); 
  } 
} 
 
// A derived class of TwoDShape for triangles. 
class Triangle : TwoDShape { 
  string style; // private 
   
  // A default constructor. 
  public Triangle() { 
    style = "null"; 
  } 
 
  // Constructor for Triangle. 
  public Triangle(string s, double w, double h) : base(w, h) { 
    style = s;  
  } 
 
  // Construct an isosceles triangle. 
  public Triangle(double x) : base(x) { 
    style = "isosceles";  
  } 
 
  // Construct an object from an object. 
  public Triangle(Triangle ob) : base(ob) { 
    style = ob.style; 
  } 
 
  // Return area of triangle. 
  public double area() { 
    return width * height / 2; 
  } 
 
  // Display a triangle's style. 
  public void showStyle() { 
    Console.WriteLine("Triangle is " + style); 
  } 
} 
 
class Shapes7 { 
  public static void Main() { 
    Triangle t1 = new Triangle("right", 8.0, 12.0); 
 
    // make a copy of t1 
    Triangle t2 = new Triangle(t1); 
 
    Console.WriteLine("Info for t1: "); 
    t1.showStyle(); 
    t1.showDim(); 
    Console.WriteLine("Area is " + t1.area()); 
 
    Console.WriteLine(); 
 
    Console.WriteLine("Info for t2: "); 
    t2.showStyle(); 
    t2.showDim(); 
    Console.WriteLine("Area is " + t2.area()); 
  } 
}

listing 16
// Demonstrate a virtual method. 
 
using System; 
 
class Base { 
  // Create virtual method in the base class.  
  public virtual void who() { 
    Console.WriteLine("who() in Base"); 
  } 
} 
 
class Derived1 : Base { 
  // Override who() in a derived class. 
  public override void who() { 
    Console.WriteLine("who() in Derived1"); 
  } 
} 
 
class Derived2 : Base { 
  // Override who() again in another derived class. 
  public override void who() { 
    Console.WriteLine("who() in Derived2"); 
  } 
} 
 
class OverrideDemo { 
  public static void Main() { 
    Base baseOb = new Base(); 
    Derived1 dOb1 = new Derived1(); 
    Derived2 dOb2 = new Derived2(); 
 
    Base baseRef; // a base-class reference 
 
    baseRef = baseOb;  
    baseRef.who(); 
 
    baseRef = dOb1;  
    baseRef.who(); 
 
    baseRef = dOb2;  
    baseRef.who(); 
  } 
}

listing 17
/* When a virtual method is not overridden, 
   the base class method is used. */ 
 
using System; 
 
class Base { 
  // Create virtual method in the base class.  
  public virtual void who() { 
    Console.WriteLine("who() in Base"); 
  } 
} 
 
class Derived1 : Base { 
  // Override who() in a derived class. 
  public override void who() { 
    Console.WriteLine("who() in Derived1"); 
  } 
} 
 
class Derived2 : Base { 
  // This class does not override who(). 
} 
 
class NoOverrideDemo { 
  public static void Main() { 
    Base baseOb = new Base(); 
    Derived1 dOb1 = new Derived1(); 
    Derived2 dOb2 = new Derived2(); 
 
    Base baseRef; // a base-class reference 
 
    baseRef = baseOb;  
    baseRef.who(); 
 
    baseRef = dOb1;  
    baseRef.who(); 
 
    baseRef = dOb2;  
    baseRef.who(); // calls Base's who() 
  } 
}

listing 18
/*  In a multilevel hierarchy, the  
    first override of a virtual method 
    that is found while moving up the 
    hierarchy is the one executed. */ 
  
using System;  
  
class Base {  
  // Create virtual method in the base class.   
  public virtual void who() {  
    Console.WriteLine("who() in Base");  
  }  
}  
  
class Derived1 : Base {  
  // Override who() in a derived class.  
  public override void who() {  
    Console.WriteLine("who() in Derived1");  
  }  
}  
  
class Derived2 : Derived1 {  
  // This class also does not override who().  
}  
 
class Derived3 : Derived2 {  
  // This class does not override who().  
}  
 
class NoOverrideDemo2 {  
  public static void Main() {  
    Derived3 dOb = new Derived3();  
    Base baseRef; // a base-class reference  
  
    baseRef = dOb;   
    baseRef.who(); // calls Derived1's who()  
  }  
}

listing 19
// Use virtual methods and polymorphism. 
 
using System; 
 
class TwoDShape {  
  double pri_width;  // private 
  double pri_height; // private 
  string pri_name;   // private 
  
  // A default constructor.  
  public TwoDShape() {  
    width = height = 0.0;  
    name = "null";  
  }  
  
  // Parameterized constructor.  
  public TwoDShape(double w, double h, string n) {  
    width = w;  
    height = h;  
    name = n;  
  }  
  
  // Construct object with equal width and height.  
  public TwoDShape(double x, string n) {  
    width = height = x;  
    name = n;  
  }  
  
  // Construct an object from an object.  
  public TwoDShape(TwoDShape ob) {  
    width = ob.width;  
    height = ob.height;  
    name = ob.name;  
  }  
  
  // Properties for width, height, and name 
  public double width { 
    get { return pri_width; } 
    set { pri_width = value; } 
  } 
 
  public double height { 
    get { return pri_height; } 
    set { pri_height = value; } 
  } 
 
  public string name { 
    get { return pri_name; } 
    set { pri_name = value; } 
  } 
  
  public void showDim() {  
    Console.WriteLine("Width and height are " +  
                       width + " and " + height);  
  }  
  
  public virtual double area() {   
    Console.WriteLine("area() must be overridden");  
    return 0.0;  
  }   
}  
  
// A derived class of TwoDShape for triangles. 
class Triangle : TwoDShape {  
  string style; // private 
    
  // A default constructor.  
  public Triangle() {  
    style = "null";  
  }  
  
  // Constructor for Triangle.  
  public Triangle(string s, double w, double h) : 
    base(w, h, "triangle") {  
      style = s;   
  }  
  
  // Construct an isosceles triangle.  
  public Triangle(double x) : base(x, "triangle") {  
    style = "isosceles";   
  }  
  
  // Construct an object from an object.  
  public Triangle(Triangle ob) : base(ob) {  
    style = ob.style;  
  }  
  
  // Override area() for Triangle. 
  public override double area() {  
    return width * height / 2;  
  }  
  
  // Display a triangle's style. 
  public void showStyle() {  
    Console.WriteLine("Triangle is " + style);  
  }  
}  
  
// A derived class of TwoDShape for rectangles.   
class Rectangle : TwoDShape {   
  // Constructor for Rectangle.  
  public Rectangle(double w, double h) :  
    base(w, h, "rectangle"){ }  
  
  // Construct a square.  
  public Rectangle(double x) :  
    base(x, "rectangle") { }  
  
  // Construct an object from an object.  
  public Rectangle(Rectangle ob) : base(ob) { }  
  
  // Return true if the rectangle is square. 
  public bool isSquare() {   
    if(width == height) return true;   
    return false;   
  }   
     
  // Override area() for Rectangle. 
  public override double area() {   
    return width * height;   
  }   
}  
  
class DynShapes {  
  public static void Main() {  
    TwoDShape[] shapes = new TwoDShape[5];  
  
    shapes[0] = new Triangle("right", 8.0, 12.0);  
    shapes[1] = new Rectangle(10);  
    shapes[2] = new Rectangle(10, 4);  
    shapes[3] = new Triangle(7.0);  
    shapes[4] = new TwoDShape(10, 20, "generic"); 
  
    for(int i=0; i < shapes.Length; i++) {  
      Console.WriteLine("object is " + shapes[i].name);  
      Console.WriteLine("Area is " + shapes[i].area());  
  
      Console.WriteLine();    
    }  
  }  
}

listing 20
// Create an abstract class. 
 
using System; 
 
abstract class TwoDShape {  
  double pri_width;  // private 
  double pri_height; // private 
  string pri_name;   // private 
  
  // A default constructor.  
  public TwoDShape() {  
    width = height = 0.0;  
    name = "null";  
  }  
  
  // Parameterized constructor.  
  public TwoDShape(double w, double h, string n) {  
    width = w;  
    height = h;  
    name = n;  
  }  
  
  // Construct object with equal width and height.  
  public TwoDShape(double x, string n) {  
    width = height = x;  
    name = n;  
  }  
  
  // Construct an object from an object.  
  public TwoDShape(TwoDShape ob) {  
    width = ob.width;  
    height = ob.height;  
    name = ob.name;  
  }  
  
  // Properties for width, height, and name 
  public double width { 
    get { return pri_width; } 
    set { pri_width = value; } 
  } 
 
  public double height { 
    get { return pri_height; } 
    set { pri_height = value; } 
  } 
 
  public string name { 
    get { return pri_name; } 
    set { pri_name = value; } 
  } 
  
  public void showDim() {  
    Console.WriteLine("Width and height are " +  
                       width + " and " + height);  
  }  
  
  // Now, area() is abstract. 
  public abstract double area(); 
}  
  
// A derived class of TwoDShape for triangles. 
class Triangle : TwoDShape {  
  string style; // private 
    
  // A default constructor.  
  public Triangle() {  
    style = "null";  
  }  
  
  // Constructor for Triangle.  
  public Triangle(string s, double w, double h) : 
    base(w, h, "triangle") {  
      style = s;   
  }  
  
  // Construct an isosceles triangle.  
  public Triangle(double x) : base(x, "triangle") {  
    style = "isosceles";   
  }  
  
  // Construct an object from an object.  
  public Triangle(Triangle ob) : base(ob) {  
    style = ob.style;  
  }  
  
  // Override area() for Triangle. 
  public override double area() {  
    return width * height / 2;  
  }  
  
  // Display a triangle's style. 
  public void showStyle() {  
    Console.WriteLine("Triangle is " + style);  
  }  
}  
  
// A derived class of TwoDShape for rectangles.   
class Rectangle : TwoDShape {   
  // Constructor for Rectangle.  
  public Rectangle(double w, double h) :  
    base(w, h, "rectangle"){ }  
  
  // Construct a square.  
  public Rectangle(double x) :  
    base(x, "rectangle") { }  
  
  // Construct an object from an object.  
  public Rectangle(Rectangle ob) : base(ob) { }  
  
  // Return true if the rectangle is square. 
  public bool isSquare() {   
    if(width == height) return true;   
    return false;   
  }   
     
  // Override area() for Rectangle. 
  public override double area() {   
    return width * height;   
  }   
}  
  
class AbsShape {  
  public static void Main() {  
    TwoDShape[] shapes = new TwoDShape[4];  
  
    shapes[0] = new Triangle("right", 8.0, 12.0);  
    shapes[1] = new Rectangle(10);  
    shapes[2] = new Rectangle(10, 4);  
    shapes[3] = new Triangle(7.0);  
  
    for(int i=0; i < shapes.Length; i++) {  
      Console.WriteLine("object is " + shapes[i].name);  
      Console.WriteLine("Area is " + shapes[i].area());  
  
      Console.WriteLine();    
    }  
  }  
}

listing 21
// Demonstrate ToString() 
 
using System; 
 
class MyClass { 
  static int count = 0; 
  int id; 
 
  public MyClass() { 
    id = count; 
    count++; 
  } 
 
  public override string ToString() { 
    return "MyClass object #" + id; 
  } 
} 
 
class Test { 
  public static void Main() { 
    MyClass ob1 = new MyClass(); 
    MyClass ob2 = new MyClass(); 
    MyClass ob3 = new MyClass(); 
 
    Console.WriteLine(ob1); 
    Console.WriteLine(ob2); 
    Console.WriteLine(ob3); 
 
  } 
}

listing 22
// A simple boxing/unboxing example. 
 
using System; 
 
class BoxingDemo { 
  public static void Main() { 
    int x; 
    object obj; 
 
    x = 10; 
    obj = x; // box x into an object 
 
    int y = (int)obj; // unbox obj into an int 
    Console.WriteLine(y); 
  } 
}

listing 23
// Boxing also occurs when passing values. 
 
using System; 
 
class BoxingDemo { 
  public static void Main() { 
    int x; 
    
    x = 10; 
    Console.WriteLine("Here is x: " + x); 
 
    // x is automatically boxed when passed to sqr() 
    x = BoxingDemo.sqr(x); 
    Console.WriteLine("Here is x squared: " + x); 
  } 
 
  static int sqr(object o) { 
    return (int)o * (int)o; 
  } 
}

listing 24
// Boxing makes it possible to call methods on a value! 
 
using System; 
 
class MethOnValue { 
  public static void Main() { 
 
    Console.WriteLine(10.ToString()); 
 
  } 
}

listing 25
// Use object to create a generic array. 
 
using System; 
 
class GenericDemo {   
  public static void Main() {   
    object[] ga = new object[10]; 
  
    // store ints 
    for(int i=0; i < 3; i++) 
      ga[i] = i; 
  
    // store doubles 
    for(int i=3; i < 6; i++) 
      ga[i] = (double) i / 2;  
 
 
    // store two strings, a bool, and a char 
    ga[6] = "Generic Array"; 
    ga[7] = true; 
    ga[8] = 'X'; 
    ga[9] = "end"; 
 
    for(int i = 0; i < ga.Length; i++) 
      Console.WriteLine("ga[" + i + "]: " + ga[i] + " "); 
 
  }  
}