2023.7.26 周三：instanceof

/*
instancof 判断两个类之间是否有继承关系
Object->String
Object->Person->Teacher
Object->Person->Student
*/
Object s1 = new Student();
System.out.println(s1 instanceof Object);//True
System.out.println(s1 instanceof Person);//True
System.out.println(s1 instanceof Student);//True
System.out.println(s1 instanceof Teacher);//False
System.out.println(s1 instanceof String);//False 
Person s2 = new Student();
System.out.println(s2 instanceof Object);//True
System.out.println(s2 instanceof Person);//True
System.out.println(s2 instanceof Student);//True
System.out.println(s2 instanceof Teacher);//False
//System.out.println(s2 instanceof String);//编译错误
Student s3 = new Student();
System.out.println(s3 instanceof Object);//True
System.out.println(s3 instanceof Person);//True
System.out.println(s3 instanceof Student);//True
//System.out.println(s2 instanceof Teacher);//编译错误
//System.out.println(s2 instanceof String);//编译错误
    
public static void main(String[] args){
    Student s = new Student();
    s.student();
    Person p = s;//子转父
    
    Person obj = new Student();
    ((Student)obj).student();//父转子
}