A generic problem ., Generic problems.

A generic problem ., Generic problems.

Some time ago, I was still wondering that in the previous design mode Singleton mode, I only updated the object once. However, I have obtained two or more different objects. Let's do a test today. The Code is as follows:

Experiments show that the object is indeed new twice, and the initial is indeed in two times. For different generic objects, the memory needs to be re-opened.

Save the following document.

Http://www.cnblogs.com/DebugLZQ/archive/2012/09/03/2669383.html

Http://msdn.microsoft.com/en-US/library/f4a6ta2h (v = vs.80). aspx

 1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5  6 namespace ConsoleApplication10 7 { 8     class Program 9     {10         static void Main(string[] args)11         {12             generictest<custom1>.List.Add(new custom1("custom1(1)"));13             generictest<custom1>.List.Add(new custom1("custom1(2)"));14             generictest<custom2>.List.Add(new custom2("custom2(1)"));15             generictest<custom2>.List.Add(new custom2("custom2(2)"));16             Console.ReadKey();17         }18     }19     class generictest<T>20     {21         private generictest()22         { }23         static private List<T> list=null;24          static public List<T> List25          {26              set27              {28 29                  list = value;30              }31              get32              {33                  if (list == null)34                  {35                      initial();36                  }37                  return list;38              }39          }40 41          private static void initial()42          {43              list = new List<T>();44          }45     }46     class custom147     {48         public  string str;49         public custom1(string str)50         { 51         this.str=str;52         }53     }54     class custom255     {56      public  string str;57         public custom2(string str)58         { 59         this.str=str;60         }61     62     }63 }

 

Teach a question about java generics

<T extends A> void test (List <T> list); indicates A type installed in the List ..

Void test (List <? Extends A> list); indicates any type ..

The difference is that a certain type is definite ..

Any type is unknown ..

It is reflected in the code ..

You are in <T extends A> void test (List <T> list); in this method .. you can retrieve the data in the list. The data type is T .. adding to it is also .. the T type can be added ..
But in void test (List <? Extends A> list) here... because it can be of any type... he does not know what type... so he cannot add... even the Object is not ..

<T> void test (List <T> list ){
T t = null;
List. add (t );
T t1 = list. get (0 );

}

Void test1 (List <?> List ){
Object obj = list. get (0); // valid
// List. add (new Object (); an error is reported. What is it installed in it? Type... not Object ..
}

Hope to help you ..

A java generic problem

<T extends Collection> the keyword extends is used here. It can be a class or an interface later. However, the extends here is no longer the meaning of inheritance. It should be understood that the T type is the type that implements the Collection interface, or T is the type that inherits the XX class.
I just found it online for you. At the beginning, I didn't see the problem clearly, so I also learned something, huh, huh, baike.baidu.com/view/1436058.htm? Func = retitle this is the URL