A little knowledge about collections

In C #, we know that there is a wildcard, such as list. You can specify various types of data for it,

 

Whether it is a value type or a reference type, you can put it in the past.

 

For example, list <int> List = new list <int> ();

 

List <string> List = new list <string> ();

 

Such definitions are legal.

 

But in Java

 

List <int> List = new arraylist <int> ();

 

This is illegal,

 

List <integer> List = new arraylist <integer> ();

 

This is legal. It may be that the list in Java can only include the reference type, but the value type cannot be used like this.