java 判断对象是否是某个类的类型方法

class Do1
{
    public static void main(String[] args)
    {
        AA a=new CC();
        if(a instanceof CC)
        {
            CC b=(CC)a;
        b.run();
        }

    }
}
class AA
{
    int y=3;
    void brun()
    {
    System.out.println(y);
    }
}

class CC extends AA
{
    int x=1;
    void run()
    {
    System.out.println(x);
    }
}
class BB extends AA
{
    int x=2;
    void run()
    {
    System.out.println(x);
    }
}