新手入门问题求解

import *
   public class abc    {
        public static void main(String args[ ])         {  
System.out.println("a="+a+"\nb="+b);   }     }
   class SubClass extends SuperClass     {  
int c;
SubClass(int aa, int bb, int cc)       {  
  super(aa, bb);         
  c=cc;       }     }
  class SubSubClass extends SubClass   {  
 int a;
      SubSubClass(int aa, int bb, int cc)   
    {   super(aa, bb, cc);           A = aa+bb+cc;        }
      void show()       {   
System.out.println("a="+a+"\nb="+b+"\nc="+c);
}   }
运行结果为a=60 b=20 c=30
麻烦大神说一下为什么 这俩个父子类具体是干嘛的