2021-05-07 package inheritance super this

encapsulation

High cohesion Low coupling
Property private get/set

The significance of encapsulation ：
Improve the security of the program , Protection data
Hide the implementation details of the code
Unified interface
System maintainability increases

Inherit

The essence of inheritance is to abstract a batch of classes , In order to achieve better modeling of the real world
extends It means to extend , A subclass is an extension of a parent

java Class has only singleton inheritance , No more inheritance

Subclass inherits parent , Use keywords extends To express

//Person  people   Parent class 
public class Person {
    
    public void say(){
    
        System.out.println(" Said a word ");
    }
}

package oop.demo5;

// Student  is  people   Subclass 
public class Student extends Person{
    
}

public class Application {
    
    public static void main(String[]args){
    
        Student student = new Student();
        student.say();
    }
}

Private things cannot be inherited （ Unless with get,set extract ）

super Be careful

1. super Call the constructor of the parent class , Must be in the first... Of the construction method
2. super Must only appear in a subclass's method or constructor
3. super and this Cannot call constructor at the same time

super VS this

Different objects represented ：
this： Calling the object itself
super： Represents the application of the parent object

Premise ：
this： You can use without inheritance
super： It can only be used under the condition of inheritance

Construction method ：
this（）： Call the constructor of this class
super（）： Call the construction of the parent class
.