Parent class reference to child class (parent class reference points to child class object)

（ I hope you can point out any mistakes , thank you .）
Use the premise ： In the relationship between parent and child classes , The method to be called should be defined in the parent class .

for example ：Animal a=new Dog();

Animal Class is Dog The parent of a class , The statement is a Animal class , In fact, it points to an object of a subclass That is to say new After the keyword .

keyword ： polymorphic , Dynamic links , Upward transformation

1、 polymorphic

Method rewriting, overloading and dynamic linking constitute polymorphism , In the reference of parent class to child class, it is mainly reflected in the override of parent method by child class

2、 Dynamic links

When a method defined in the parent class is not overridden in the subclass , It's called the method of the parent class , If the subclass has a new method for the parent class , Then the method of the subclass is called .

3、 Upward transformation

In the example , In fact, it instantiates a subclass Dog Object of type ,Animal The parent of type a Just a quote from him
therefore Animal A reference to a type can point to Dog Type of object . This is it. “ Upward transformation ”

public class Animal {
    
    public  void animal1(){
    }
    public void animal2(){
    }
}

public class Dog extends Animal {
    public  void animal1(){
        System.out.println(" Inherited parent class   And rewrite his method ");
    }
    public void animal1(String dog){
        System.out.println(" Here is the right animal1() Method overloading .");
    }

    public static void main(String[] args) {
     Animal a=new Dog();
     a.animal2();// Here animal3() Method calls the method of the parent class 
     a.animal1();// This is because animal1() Method , So the reference of the parent type can call this method 
     a.animal1("sss");// The error here is because there is no definition in the parent class animal1(String dog) The method ,
                      //  This method is only for animal1() An override of method , So a reference of a parent type cannot call this method 
    }
}