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
*/
