static void Main()
{
int j = new int(); //值类型。哟i一个默认的无参数的构造函数。这个与int j;等价
RefSample <int> re = new RefSample <int>();
CreatAnInstance <string> re2 = new CreatAnInstance <string>(); //不接受单个字符串的构造函数
StreamReader <DerivedClass> dd = new StreamReader <DerivedClass>();
//System.String h = new String("D");//string不存在默认的构造函数
//StreamReader<string> dd2 = new StreamReader<string>();//new()是失败的
TypeDeduce.Change <object>(251);//派生类向基类的转换
//TypeDeduce.Change<int>((object)25);//禁止反向转换
}
// C#2:解决C#1的问题
/*
* 理解泛型类型和方法
* 泛型方法的类型推断
* 类型约束
* 反射和泛型
* CLR行为
* 泛型的限制
* 与其他语言对比
*/
static void Main(string[] args)
{
string text = @"Do you like green eggs and ham?I do not like them, Sam-I-am.I do not like green eggs and ham.";
Dictionary <string, int> frequencies = CountWords(text);
foreach (var entry in frequencies)
{
//不用强转，避免装箱拆箱的性能损耗。
string word = entry.Key;
int frequency = entry.Value;
Console.WriteLine("{0}: {1}", word, frequency);
}
Console.WriteLine("xixi");
List <int> ints = new List <int>();
ints.Add(1);
ints.Add(2);
ints.Add(3);
ints.Add(4);
Converter <int, double> converter = TakeSquareRoot;
List <double> doubles;
doubles = ints.ConvertAll(converter);
foreach (var d in doubles)
{
Console.WriteLine(d);
}
Console.WriteLine("*******");
List <string> list = MakeList("line1", "line2");
foreach (var li in list)
{
Console.WriteLine(li);
}
Console.WriteLine("*******");
RefSample <string> refSample = new RefSample <string>();
RefSample <string> refSample1 = new RefSample <string>();
//if (refSample)
//{
// Nullable<int> int1 = 1;
//}
Console.WriteLine(refSample.GetType().IsByRef);
Console.WriteLine();
Console.WriteLine("***Default value for T, could compare any type that implemented IComparable with default value.***");
Console.WriteLine("***bigger 1, equal 0, less -1***");
Console.WriteLine(CompareToDefault("x"));
Console.WriteLine(CompareToDefault(10));
Console.WriteLine(CompareToDefault(0));
Console.WriteLine(CompareToDefault(-10));
Console.WriteLine(CompareToDefault(DateTime.MinValue));
string name = "Jon";
string intro1 = "My name is " + name;
string intro2 = "My name is " + name;
//使用string重载的==操作符进行比较
// Determines whether two specified strings have the same value.
Console.WriteLine(intro1 == intro2);
Console.WriteLine(AreReferencesEqual(intro1, intro2));
Pair <int, string> pair1 = new Pair <int, string>(10, "value");
Pair <int, string> pair2 = Pair <int, string> .Of(10, "value");
Console.WriteLine("***证明不同的封闭类型具有不同的静态字段***");
TypeWithField <int> .field = "First";
TypeWithField <string> .field = "Second";
TypeWithField <DateTime> .field = "Third";
TypeWithField <int> .PrintField();
TypeWithField <string> .PrintField();
TypeWithField <DateTime> .PrintField();
Console.WriteLine("***C#1:一个完整的泛型枚举--从0枚举到9***");
CountingEnumerable counter = new CountingEnumerable();
foreach (var x in counter)//1.首先调用MoveNext方法。 2.获取Current的值。
{
Console.WriteLine(x);
}
Console.WriteLine("***对类型参数使用typeof操作符***");
DemonstrateTypeof <int>();
Console.WriteLine("***获取泛型和已构造Type对象的各种方式***");
string listTypeName = "System.Collections.Generic.List`1";
Type defByName = Type.GetType(listTypeName);
Type closedByName = Type.GetType(listTypeName + "[System.String]");
Type closedByMethod = defByName.MakeGenericType(typeof(string));
Type closedByTypeof = typeof(List <string>);
Console.WriteLine(closedByMethod == closedByName);
Console.WriteLine(closedByName == closedByTypeof);
Type defByTypeof = typeof(List <>);
Type defByMethod = closedByName.GetGenericTypeDefinition();
Console.WriteLine(defByMethod == defByName);
Console.WriteLine(defByName == defByTypeof);
Console.WriteLine("***通过反射来获取和调用泛型方法***");
Type type = typeof(Snippet);
MethodInfo definition = type.GetMethod("PrintTypeParameter");
MethodInfo constructed = definition.MakeGenericMethod(typeof(string));
constructed.Invoke(null, null);
Console.WriteLine("***泛型可变性的缺乏***");
//Animal[] animals = new Cat[5];//编译通过，但会在运行时出现写入错误
//animals[0] = new Turtle();//“System.ArrayTypeMismatchException”类型的未经处理的异常在 3_GenericParameterizedType.exe 中发生
//List<Animal> animals = new List<Cat>();//编译不通过
Console.ReadKey();
}
