Body2.java

public final class Body2  {

   static long nextID = 0;
   long idNum;
   String nameFor;
   Body2 orbits;

   Body2 () {
      idNum = nextID++;
   }

   public static void main (final String[] args)  {
      final Body2 sun   = new Body2();
      sun.idNum   = Body2.nextID++;
      sun.nameFor = "Sol";
      sun.orbits  = null;        // "Sol" orbits no body

      final Body2 earth   = new Body2();
      earth.idNum   = Body2.nextID++;
      earth.nameFor = "Earth";
      earth.orbits  = sun;
   }
}