public class Base{    private  String baseName = "base";    public Base()    {        callName();    }     public void callName()    {        System. out. println(baseName);    }     static class Sub extends Base    {        private String baseName = "sub";        public void callName()        {            System. out. println (baseName) ;        }    }    public static void main(String[] args)    {        new Sub();            }}

输出结果为null

求解