多态及instanof的引用类型

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

        //一个对象的实际类型是确定的
        //new Student();
       //new Person();

        //可以指向的引用类型就不确定了：父类的引用指向子类

        //Student 能调用的方法都是自己的或者继承父类的！
        Student s1=new Student();
        //Person 父类型，可以指向子类，但是不能调用子类独有的方法
        Person s2=new Student();
        Object s3=new Student();

        //对象能执行哪种方法，主要看对象左边的类型，和右边关系不大
        ((Student) s2).eat();  //子类重写了父亲的方法，执行了子类的方法
        s1.run();
    }
}

public class Student extends Person{
    @Override
    public void run() {
        System.out.println("son");
    }
    public void eat(){
        System.out.println("eat");
    }
}

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

        //类型之间的转换：父    子

        //高                   低
        //Person obj=new Student();
        //student将这个对象转换为Student类型，我们就可以使用Student类型的方法了！
        //((Student) obj).go();

        //子类转换为父类，可能丢失自己本来的一些方法！
        Student student=new Student();
        student.go();
        Person person=student;
    }
}

public class Student extends Person{
    public void go(){
        System.out.println("go");
    }
}


/*
//Obect > String
        //Object >Person > Teacher
        //Object >Person > Student
        Object object=new Student();

        //System.out.println(X instanceof Y); //X与Y是否存在父子关系，判断是否编译通过！

        System.out.println(object instanceof Student);//true
        System.out.println(object instanceof Person);//true
        System.out.println(object instanceof Object);//true
        System.out.println(object instanceof Teacher);//false
        System.out.println(object instanceof String);//false
        System.out.println("================");
        Person person=new Student();
        System.out.println(person instanceof Student);//true
        System.out.println(person instanceof Person);//true
        System.out.println(person instanceof Object);//true
        System.out.println(person instanceof Teacher);//false
        //System.out.println(person instanceof String);//编译报错！
        System.out.println("================");
        Student student=new Student();
        System.out.println(student instanceof Student);//true
        System.out.println(student instanceof Person);//true
        System.out.println(student instanceof Object);//true
        //System.out.println(student instanceof Teacher);//false
        //System.out.println(student instanceof String);//编译报错！
 */