instanceof和类型转换

instanceof：判断一个对象是什么类型

public class Person {
    public void run(){
        System.out.println("ss");
    }
}

public class Student extends Person {

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

}

public class Teacher extends Person {
}

public static void main(String[] args) {

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

    //System.out.println(x instanceof y);//能不能编译通过！

    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);//编译报错
    //System.out.println(student instanceof String);//编译报错
}

类型转换：

1.父类的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；需要强制转换

4.方便方法的调用，减少重复的代码！简介

**抽象：封装、继承、多态 **

抽象类，接口

  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 student=(Student)obj;
//        ((Student)obj).go();


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

    }