instanceof

package com.oop.demo06;

public class Person {
    
}
//==========================
package com.oop.demo06;
public class Teacher extends Person {

}
//===========================
package com.oop.demo06;
public class Student 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 > Person > Student
        //Object > Person > Teacher
        //Object > String
        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
    }
}

类型转换

//====================================
//类型转换
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) {
        //类型之间的转换：父   子
        //      高              低
        Person person = new Student();
        //将person这个对象转换为Student类型，就可以使用Student类型的方法了
        Student student = (Student) person;
        student.go();
        //或者写成下边形式
        ((Student) person).go();
        
        //-------------------------------------------------
        //子类转换为父类，可能会丢失一些方法！
        Student student = new Student();
        student.go();
        Person person = student;
        ((Student) person).go();
    }
}


//--------------------------------------
package com.oop.demo06;

public class Person {
    public void run(){
        System.out.println("run");
    }
}
//--------------------------------------
package com.oop.demo06;

public class Student extends Person {
    public void go(){
        System.out.println("go");
    }
}
/*
多态：
1.父类引用指向子类的对象
2.把子类转换为父类，向上转型
3.把父类转换为子类，向下转型；强制转换
4.方便方法的调用，减少重复的代码！ 简洁

抽象 ： 封装、继承、多态
 */