What is generics and how to use generics analysis

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1、 Generic

1： What is generics ？

Generics are broad types , It's also a data type , This data type can be any type , The type cannot be determined during writing , You must specify a specific type when creating an object , You can't specify , But there will be some mistakes .

Generics are compiler behavior , Only valid at compile time , If you can cross the compiler , Then generics make no sense .

2、 Generic classes

How to define generic classes ？

Add after class <>,<> You can write any length and any character in , Cannot be numeric .（ It's usually used 26 Capital English letters indicate ）

Generic classes < The specific type > Variable name = new Generic classes <>();

Code example ：

3、 Generic interface

Implementation classes do not specify generic types when implementing generic interfaces In this case, the generic type can be specified when creating the implementation class object class UserServiceImpl<T> implements UserService<T> The implementation class specifies the generic type when implementing the generic interface Then the generic type will be determined class UserServiceImpl implements UserService<String>

Code example ：

4、 Generic methods

Method This method is a generic method Static methods cannot use generic types declared in generic classes Because the generic type is determined when the object is created , Static methods exist before objects , If you want to use , Declare a generic type on the current static method public static < The generic type > void Method name ()

Code example ：

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