使用 as 和 is 运算符安全地进行强制转换

class SafeCasting 
{ 
    class Animal 
    { 
        public void Eat() { Console.WriteLine("Eating."); } 
        public override string ToString() 
        { 
            return "I am an animal."; 
        } 
    } 
    class Mammal : Animal { } 
    class Giraffe : Mammal { } 
 
    class SuperNova { } 
 
    static void Main() 
    { 
        SafeCasting app = new SafeCasting(); 
 
        // Use the is operator to verify the type. 
        // before performing a cast. 
        Giraffe g = new Giraffe(); 
        app.UseIsOperator(g); 
 
        // Use the as operator and test for null 
        // before referencing the variable. 
        app.UseAsOperator(g); 
 
        // Use the as operator to test 
        // an incompatible type. 
        SuperNova sn = new SuperNova(); 
        app.UseAsOperator(sn); 
 
        // Use the as operator with a value type. 
        // Note the implicit conversion to int? in  
        // the method body. 
        int i = 5; 
        app.UseAsWithNullable(i); 
 
 
        double d = 9.78654; 
        app.UseAsWithNullable(d); 
 
        // Keep the console window open in debug mode. 
        System.Console.WriteLine("Press any key to exit."); 
        System.Console.ReadKey(); 
    } 
 
    void UseIsOperator(Animal a) 
    { 
        if (a is Mammal) 
        { 
            Mammal m = (Mammal)a; 
            m.Eat(); 
        } 
    } 
 
    void UseAsOperator(object o) 
    { 
        Mammal m = o as Mammal; 
        if (m != null) 
        { 
            Console.WriteLine(m.ToString()); 
        } 
        else 
        { 
            Console.WriteLine("{0} is not a Mammal", o.GetType().Name); 
        } 
    } 
 
    void UseAsWithNullable(System.ValueType val) 
    { 
        int? j = val as int?; 
        if (j != null) 
        { 
            Console.WriteLine(j); 
        } 
        else 
        { 
            Console.WriteLine("Could not convert " + val.ToString()); 
        } 
    } 
}