Internal class (detailed explanation of four internal classes)

== = = = = = = Inner class （ Detailed explanation of four internal classes ）= = = = = = = ==

One 、 Basic introduction ： Another class structure is completely nested inside a class . Nested classes are called inner classes (inner class), Classes that nest other classes are called outer classes (outer class). Is the fifth largest member of our class 【 reflection : What are the five members of a class ?[ attribute 、 Method 、 Constructors 、 Code block 、 Inner class ]】, The biggest feature of internal classes is that they can directly access private properties , And it can reflect the inclusion relationship between classes , Be careful : Internal classes are the difficulty of learning , It's also the point , When looking at the underlying source code later , There are a lot of inner classes .
If the definition class is in a local location ( In the method / Code block ) :(1) Local inner classes (2) Anonymous inner class
Defined in the member location (1) Member inner class (2) Static inner class

Two 、 Basic grammar
class Outer{ // External class
class Inner{ // Inner class
}
}
class Other{ // External other classes
}

3、 ... and 、 Classification of internal classes
Defined in the local location of the external class ( As in method ):
1) Local inner classes ( Class name )
2) Anonymous inner class ( No class name , a key !!!)
· Defined in the member position of the external class :
1) Member inner class ( useless static modification )
2) Static inner class （ Use static modification )

1、 Local inner classes
explain : A local inner class is defined in a local location of an outer class , For example, in the method , And have a class name .
1. You can directly access all members of an external class , Include private
2 Cannot add access modifier , Because its status is a local variable . You can't use modifiers for local variables . But you can use final modification , Because local variables can also be used final
3. Scope : Just in the method or code block that defines it .
4. Local inner classes — visit ----> Members of external classes [ access : Direct access ]
5. External class — visit ----> Members of local inner classes
access : Create objects , Revisit ( Be careful : Must be in scope )
remember :
(1) Local inner classes are defined in methods / Code block
(2) The scope is in the method body or code block
(3) The essence is still a class
6. External other classes — Cannot access -----> Local inner classes （ Because the local internal class status is a local variable )
7. If the members of the external class and the local internal class have the same name , By default, follow the principle of proximity , If you want to access members of an external class , You can use ( External class name .this. member ) To visit
8. External classes in methods , You can create Inner class object , Then you can call the method

2、 Anonymous inner class
(1) The essence is class
(2） Inner class
(3) This class has no name
(4) It's also an object
explain : Anonymous inner classes are defined in outer classes
Local location of , For example, in the method , And no class name
1. The basic syntax of anonymous inner classes
new Class or interface ( parameter list ){
The class body
};

① The syntax of anonymous inner classes is strange , Please pay attention , Because the anonymous inner class is both the definition of a class , At the same time, it is also an object itself , So in terms of grammar , It has the characteristics of defining classes , There are also features of creating objects ,, So you can call anonymous inner class methods .
②. You can directly access all members of an external class , Include private
③ Cannot add access modifier , Because its status is a local variable
④ Scope : Just in the method or code block that defines it .
⑤ Anonymous inner class — visit ----> External class members [ access : Direct access ]
⑥ External other classes — Cannot access -----> Anonymous inner class （ Because anonymous inner class status is a local variable )
⑦ If the members of the outer class and the anonymous inner class have the same name , Anonymous inner class access , By default, follow the principle of proximity , If you want to access members of an external class , You can use ( External class name .this. member ) To visit

3、 Member inner class
explain : The inner class of a member is defined in the member position of the outer class , And there's no static modification .
1. You can directly access all members of an external class , Include private
2. You can add any access modifier (public、protected、 Default 、private), Because its land
Bit is a member .
3. The scope is the same as other members of the external class , For the entire class body , Create a member inner class object in the member method of the outer class , Call the method again .
4. Member inner class — visit ----> External class members ( such as ; attribute )[ access : Direct access ]
5. External class — visit ------> Member inner class access : Create objects , Revisit
6. External other classes — visit ----> Member inner class
7. If the members of the outer class and the inner class have the same name , Internal class access , By default, follow the principle of proximity , If you want to access members of an external class , You can use ( External class name .this. member ) To visit

4、 Static inner class
explain : The static inner class is defined in the member position of the outer class , And there are static modification
1. You can directly access all static members of the external class , Include private , But you can't directly access non static members
2. You can add any access modifier (public、protected、 Default 、private), Because its status is a member .
3. Scope : With other members , For the entire class body
4. Static inner class — visit ----> External class ( such as : Static attribute )[ access : Direct access to all static members ]
5． External class — visit ------> Static internal class access mode : Create objects , Revisit
6． External other classes — visit -----> Static inner class
7． If the members of the external class and the static internal class have the same name , When static inner classes are accessed , By default, the nearest... Is followed
principle , If you want to access members of an external class , You can use ( External class name . member ) To visit