2021-05-11 instanceof and type conversion

public class Application {
    
    public static void main(String[]args){
    

        Object object = new Student();

        System.out.println(object instanceof Student);
        System.out.println(object instanceof Person);
        System.out.println(object instanceof Object);
        System.out.println(object instanceof Teacher);
        System.out.println(object instanceof String);

        // Conversion between types ： Father   Son 
        // high   low 
        Person obj = new Student();
        //student Convert this object to Student type , We can use Student Type of method 

        Student student = (Student) obj;
        student.go();

        //==（（Student）obj）.go();

        // The subclass is converted to a parent class , You may lose some of your original methods 
        Student student1 = new Student();
        student.go();
        Person person = student1;
        
        
    }
}

1. Parent class reference refers to the object of the parent class
2. Convert a subclass to a parent , Upward transformation
3. Convert a parent class to a child class , Move down ： Coercive transformation
4. Convenient method call , Reduce duplicate code , concise
5. abstract ： encapsulation Inherit polymorphic