Hi all,
I have a question.  I would appreciate it if anyone could help me out.
I have made 3 array lists.  And now i want to calculate the average of
each array list.  But my getAverage method calculate cumulatively, so
when i print the list of heavy (or light) antlist then it works well.
it only prints the number of ants in the heavy (or light ) antlists.
But as for average weight, it calculates cumulatively, in other words,
it calculates all the ants in the three lists.  Does anyone know why it
happens?  Thank you in advance.

import java.util.*;

public class Main {
   // define class variables
   public static int   nextID = 0;  // unique ID number for instances
   public static int   numberOfAnts = 32,  cnt = 0;;  // answer 0
   public static double averageWeight = 0, sumWeight = 0;

   public static void main ( String args[] ) {
    Ant anAnt, anAnt1; // temp variables to hold address of Ant instance
                Random rng = new Random();  // a rng

               ArrayList <Ant> antList = new ArrayList <Ant> ();
    ArrayList <Ant> heavyAntList = new ArrayList <Ant> ();
    ArrayList <Ant> lightAntList = new ArrayList <Ant> ();

              System.out.printf( "\nCreate %d ants...", numberOfAnts
);

              for ( int i = 0; i < numberOfAnts; ++i ) {
                       anAnt = new Ant ( 4*rng.nextDouble() );
                       antList.add( anAnt );
               }
    System.out.printf( "Created %d ants. The are:\n", antList.size() );
               for ( int i = 0; i < antList.size(); ++i ) {
           (antList.get( i )).printSelf();
               }

               Main.getAverage( antList );
    System.out.printf( "\nNow sort the ants depending on their weight.\n"
);
    for ( int i = 0; i < antList.size(); ++i ) {
       Ant a = antList.get ( i );
       if ((a.getWeight()) > averageWeight ) {
       heavyAntList.add( a );
      } else {
           lightAntList.add( a );
      }
    }
               System.out.printf( "The heavy ants are :\n" );
    Main.printAntList( heavyAntList );
    Main.getAverage( heavyAntList );
    System.out.printf( "\nThe light ants are :\n" );
    Main.printAntList( lightAntList );
    Main.getAverage( lightAntList );
....

   public static void printAntList ( ArrayList <Ant> list ) {
    for ( int i = 0; i < list.size(); ++i ) {
       Ant a = list.get( i );
               System.out.printf( "%d  ID = %d, weight = %.3f\n", i,
a.getID(), a.getWeight() );
    }
   }
   public static void getAverage ( ArrayList <Ant> list ) {
    for ( int i = 0; i < list.size(); ++i ) {
       Ant a = list.get( i );
               sumWeight += a.getWeight();
    cnt = cnt + 1 ;
    averageWeight = sumWeight / cnt;
    }
   System.out.printf( "sum=%.3f, the number of ants=%d,", sumWeight,
cnt);
   System.out.printf( " Average weight=%.3f", averageWeight);
   }  
}