instanceof和类型转换

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

public class Student extends People{
	public void go(){
        System.out.println("go");
	}
}

public class Teacher extends People{
}

　

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

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

        System.out.println(object instanceof Student);//true
        System.out.println(object instanceof People);//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("====================================");

        People people = new Student();
        System.out.println(people instanceof Student);//true
        System.out.println(people instanceof People);//true
        System.out.println(people instanceof Object);//true
        System.out.println(people instanceof Teacher);//false
       // System.out.println(people 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 People);//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

public class Application {
    public static void main(String[] args) {
​
        //类型之间的转化：  父      子
        //高          低
        People obj = new Student();
        
        //如果obj将People类型转化为Student类型，我们就可以使用Student类型的方法了！
        ((Student)obj).go();
        
        //子类转换为父类，可能丢失自己的本来的一些方法！
        //低        高
        Student student = new Student();
        student.go();
        People people = student;
        //people.go();
        
   }
}

总结：

​ 　　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；强行转换

​　　 4.方便方法的调用，减少重复的代码！