Day_ ten

1.This

1.1

this: Is in each object , A reference type variable that holds its own memory address
       this It means that the current object

1.2

What can be done :1. In a member method or constructor , Distinguish between member variables and local variables with the same name
                    this.xxx
         2. In the constructor , Overload calls other constructor methods in the current class , But it must be written in the first line of the constructor
                    this(xxx)
         3.return this   Returns the memory address of the current object , You can chain call
  Who calls this member method ,this Who is the
  Be careful this Cannot use static methods

1.3 How to use it?

1.3.1 Distinguish between members and parts

 

 

 

 

 1.3.2 Overloaded call constructor

 

1.3.3 call chaining

 

 1.4 Be careful

This Cannot appear in a static context

2.Static

2.1 What is it?

Modifier , keyword , Used to distinguish between static and member

2.2 What can be done

 

2.3 Static statement block

 

2.4 Instance statement block

 

 

 3. encapsulation

Put all the components together , You can also hide the data through the permission control modifier , It can control the modification degree of class data by users

Proper encapsulation can make the code easier to understand , Easy to maintain , It improves the security of the code

3.1 Packet mechanism

3.1.1Package

 

3.1.2Import

 

Be careful : By space Or when you return the train Automatic package Guide , If the program is OK , But the report is wrong , You can see

Check to see if there is a package import error

 

3.2     Access control

 

 

 

4. Inherit

4.1 What is it?  

 

4.2 What can be done

 

4.3 How to use it?

  grammar : class Class name extends Parent class name { The class body }

 

 

 

5.Super

5.1 What is it?

 super : The official saying is   Represents the characteristics of the parent class

5.2 What can be done

 

5.3 How to use it?

5.3.1 Distinguish attributes with the same name of parent and child classes

 

 

 5.3.2 Call the father's constructor

 

 

 

 5.4 Be careful

If in the subclass constructor , No display appears super() It didn't show up this(xxx)   be There is one by default super() Call the parent nonparametric construct

also super(xxx) Must appear in subclass constructor first line   therefore this(xxx) and super(xxx) Not at the same time

Because the first line of the construction method has super() Call the parent class construct , therefore If the constructor of a class is privatized , Then the class will no longer be inherited

6. overwrite / rewrite

6.1 What is it?

 

  overwrite Specific member method , That is to say Only member methods You can override  

6.2 Application scenarios

When the function of the parent class cannot meet the needs of the child class , Overwrite .