What 's the difference between a list and a list? That is, the difference between the type parameter " " and the unbounded wildcard character ""

Difference between type parameter "<T>" and "<?>" of unbounded wildcard characters

To discuss "<T>" and "<?>", first distinguish between two different scenarios:

First, declare a generic class or generic method. Second, use a generic class or generic method. The type parameter "<T>" is primarily used for the first, declaring a generic class or generic method.
The unbounded wildcard "<?>" is primarily used for the second, using generic classes or generic methods.

In layman's parlance, "T" is what is declared when a class or method is defined, "?" Is something that is passed in at the time of the call, and the two are different concepts.