Teacher t3 = new Teacher("张三", 100, 100, 100);

 1     class Person
 2     {
 3         public void SayHello()
 4         {
 5             Console.WriteLine("我是人类");
 6         } 
 7     }
 8 
 9     class Student : Person
10     {
11         public new void SayHello()//彻底隐藏了父类的SayHello()
12         {
13             Console.WriteLine("我是学生");
14         }
15     }

 1     class Program
 2     {
 3         static void Main(string[] args)
 4         {
 5             ItemFactory<Teacher> itemFactory = new ItemFactory<Teacher>();
 6             //此处编译器会检查Teacher是否具有公有的无参构造函数。
 7             Console.WriteLine($"{itemFactory.GetNewItem().Name} ID is {itemFactory.GetNewItem().Id}");
 8 
 9             Console.ReadKey();
10         }
11     }
12     public class Teacher
13     {
14         public int Id { get; set; }
15         public string Name { get; set; }
16 
17         public Teacher()
18         {
19             Id = 1;
20             Name = "张三";
21         }
22 
23         public Teacher(int id, string name)
24         {
25             this.Id = id;
26             this.Name = name;
27         }
28     }
29 
30     class ItemFactory<T> where T : new()
31     {
32         public T GetNewItem()
33         {
34             return new T();
35         }
36     }