Internal learning

Classification of internal classes ： Member inner class （ Static inner class and non static inner class ）, Local inner classes don't talk about modifiers , Anonymous inside
class .
1. Member inner class
A member inner class is equivalent to a member of a class ：
Different from the outer class , Inner classes can be declared as private perhaps protected;
You can call members of external classes .
The inner class of the member is the member of the class ：
You can define attributes in internal classes , Method , Constructors, etc
Can be declared as abstract class , So it can be inherited by other inner classes
Can be declared as final Of
Generate external classes after compilation $ Inner class .class Bytecode file ( Applicable to local inner classes )
Be careful ：
1. Not static Members in inner classes cannot be declared as static Members of , Only in external classes or static Can only be declared in a member's inner class static member .
2. External classes access members, members of inner classes , Inner class object . The way members are .
3. Member inner classes can directly use all members of outer classes , Including private data
Inner classes can be declared as abstract classes , So it can be inherited by other inner classes , You can also state final Of .
Why use inner classes ： Each inner class can independently inherit a （ Interface , abstract class ） Internship , So whether or not the outer class has inherited a certain （ Interface , abstract class ） Realization , No effect on inner classes . Sometimes in program design, there are some problems that are difficult to solve using interfaces , At this time, you can make use of the , The ability to inherit multiple concrete or abstract classes . Interface only solves most problems , The inner class makes the solution of multiple inheritance more complete . The biggest advantage of using inner classes is that it can solve the problem of multiple inheritance very well .
（ The static ） Member inner class ：

Outer outer=new Outer();
Outer.Inner inner=outer.new Inner();

（ static state ） Member inner class ：

 Outer.Inner inner=new Outer.Inner();

2. Local inner classes
Local class scope : Code block , Constructors , Method .
The local class is still a separate class , After compilation, the inner class will be compiled to be independent .class file , But the front is preceded by the outside
Class name and $ Symbol , And numbers .
Local inner classes and local variables have similar status , Out of commission public,protected, default ,private
Local inner classes cannot use static modification , So you can't include static members either
Local inner classes can use members of external classes , Including private
Local inner classes can use local variables of external methods , But it must be final Of . It consists of declarations of local inner classes and local variables
Due to different periods .
3. Anonymous inner class
An anonymous class , Is a class without a name , Its name is given by Java Given by compiler , Anonymous classes cannot use any keywords and access control characters , The access rules of anonymous classes and local classes are the same .

interface Inner {
    
    void say();
}
public class Test{
    
    public static void main(String[] args) {
    
        person(new Inner(){
    
            @Override
            public void say() {
    
                System.out.println("java");
            }
        });
    }
    public static void person(Inner an){
    
        an.say();
    }
    }