I am a newbie in Java. I have done this following program using extend keyword in Java.I am using Netbeans Ide.My below program is correct it is given on the book Programming with JAVA by E Balagurusamy.

package room;   public class Room {  int length;  int breadth;   Room(int x, int y){      length=x;      breadth=y;  }  int area()  {      return (length*breadth);  }   class BedRoom extends Room{      int height;       BedRoom(int x,int y,int z){          super (x , y);                   height=z;      }       int volume()      {          return (length*breadth*height);      }  }   class InherTest{       public static void main (String [] args){           Bedroom room1 =new BedRoom(14,12,10);                  int area1=room1.area();                  int volume1=room1.volume();                  System.out.println("Area1="+area1);                  System.out.println("Volume="+volume);      }  } 

now my question is there is an error on line public static void main (String [] args)

and the error is:

Illegal static declaration in inner class Room.InherTest   modifier 'static' is only allowed in constant variable declarations 

What is the meaning of this error?

and how to solve the error?