Generics: a definite type of work to be postponed until the time to create an object or method call before going to clear type, parameter types, the type passed as a parameter the same.
format:
<Data Type>
Data type can only be referenced here
benefit:
A: The problem is running ahead of time to compile
B: Avoid cast
C: optimized programming to solve the yellow warning line
Generic class
The generic class defined in the
Format: public class name of the class <generic type 1, ....>
Note: The generic type must be a reference type
Generic method
The generic method defined in
Format: public <generic type> method Name Return Type <generic type>
Generic Interface
The generic definition of the interface
Format: public interface interface name <generic type 1, ........>
When the implementation class that implements the interface
The first case: already know what type of a
The second situation: do not know what type of
Senior generic (wildcard)
Generic wildcard <?>
Any type, if not explicitly, then that Object as well as any of the java class.
？ extends E
Defining downwardly, E and its subclasses
? overcome
Upwardly defined, E and its parent
You must be consistent when writing generic