instanceof

• instanceof （类型转换）引用类型，判断一个对象是什么类型

`

//Object>Person>Student
//Object>Person>Teacher
//Object>String

//System.out.println(X instanceof Y);存在父子关系编译通过
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

`

`

//父类
public class Person {
public void run(){
System.out.println("sjy");
}
}
============================
//子类
public class Student extends Person{
public void go(){
System.out.println("go");
}
}
============================
public class Application {
public static void main(String[] args) {
//类型之间转换 父 子
Person obj = new Student();
//student将这个对象转换为Student类型 ，就可以调用student类型的方法了
((Student)obj).go();//强转

//子类型转换为父类有可能丢失一些方法
Student student = new Student();
student.go();
Person person=student;

}
}

/*
1.父类引用指向子类对象
2.把子类转换为父类，向上转型
3.把父类转化为子类，向下转型 需要强制转换 有可能丢失方法
4.方便方法调用，减少重复代码

抽象：封装 继承 多态
* */
`