java基础

package com.oop.demo06;


public class Person {

    public void run() {
        System.out.println("Person->run");
    }
}

package com.oop.demo06;


public class Student extends Person{

}

package com.oop.demo06;


public class Teacher extends Person {
}

package com.oop;



import com.oop.demo06.Person;
import com.oop.demo06.Student;
import com.oop.demo06.Teacher;


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

        //Object>String
        //Object>Person>Teacher
        //Object>Person>Student
        Object object = new Student();
        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);//编译报错
//        System.out.println(student instanceof String); //编译报错

        //总结：System.out.println(X instanceof Y);编译能否通过，看X是否是Y的子类型

    }
}

package com.oop.demo06;


public class Person {

    public void run() {
        System.out.println("Person->run");
    }
}

package com.oop.demo06;


public class Student extends Person{

    public void go() {
        System.out.println("go");
    }
}

package com.oop.demo06;


public class Teacher extends Person {
}

package com.oop;
import com.oop.demo06.Person;
import com.oop.demo06.Student;



public class Application {
    public static void main(String[] args) {
        //类型之间的转化： 父   子

        //子类转化成父类，可能丢失自己的本来的一些方法！
        Student student = new Student();
        student.go();
        Person person = student;
    }
}