Class Polyhedron
public abstract class Polyhedron {
   protected int nFaces, nVertices, nEdges;
   protected double width, length, height;
   public void describe() {
     System.out.println("This polyhedron has "
     + nFaces + " faces, " + nVertices +
     " vertices, and " + nEdges + " edges. Its volume is "
     + volume());
   }
   public abstract double volume();
}