About anonymous inner classes

Let's start with an example



requirement ： stay BB class AA Class object

Read this question carefully , You may find that he is very cunning
First , The two classes are under different packages . This is normal and common , The key is AA Class has only one constructor , and , His modifier is protected, Did you learn java Our friends should know ,protected The modifier represents that calls cannot be accessed under different packages
All the questions are coming , How to create this AA What about objects? ？

There are two solutions ：

1. Will be AA Modifier of constructor in class , Change to a wider range public
2. Is to use today's focus
   
   
   First , For the first method , This method is probably the one most people think of , This method is really direct violence , But , If you put AA Class transfer source code ？ We have no way to modify the source code , All this approach has certain limitations , Not an option

then , That's the second way , Maybe it was a little strange at first 《 What the hell is this ？》
In another form, it may be clear and familiar

This is actually our anonymous inner class

So the next question is , Why use the form of anonymous inner class ？

First , We have to make sure , This
Or a AA Class ？


You can see , It is no longer a AA The class , So what is he ？
In fact, he looks like this , We should know that the object name of the anonymous inner class is not taken by us , The system helped us get it , All generally speaking, it looks a little strange

In fact, he is AA A subclass of class
We can do it in AA Class to prove

The fact is as we have proved , He's really a AA Subclasses of
Empathy , If AA Class is an interface, so its anonymous inner class should look like this

OK, next question
That is why anonymous inner classes can call AA Class protected What about the constructor ？

We can refer to this structure and think about

Since he is a AA Subclasses of classes , So what characteristics should he have ？
First , As a class , Without declaring a constructor , The system will assign an empty parameter constructor to the object by default
then , As a subclass , In the first line of the constructor , The system will also call the null parameter constructor of the calling parent class by default ！！！ It's called super（）
therefore , In fact, he looks like this

Because of the call super（）, So he took it for granted to call the null parameter constructor of the parent class , That is to say AA Class protected Decorated null parameter constructor

Because the subclass calls the method attribute of the parent class, the method constructor should , All in this way , You have crossed the limit of the permission modifier

Empathy , If we pass in a parameter （ Or more ）, But then , The system will not allocate null parameter constructors , Instead, you can directly call the constructor in the child or parent class that matches it