Data Structures, Algorithms, & Applications in Java
Chapter 18, Exercise 13

We shall assume that the profits and weights are of type double. First we define a class Element which is used to sort the objects into nondecreasing order of profit density. Following the sort, the objects are to be packed into the knapsack in the reverse of this order. The method greedyKnapsack packs the objects into the knapsack in nonincreasing order of profit density. It returns the profit generated by the greedy packing. It also sets x[i] to 1 if object i is packed into the knapsack and to 0 if object i is not packed into the knapsack. 
public class GreedyKnapsack
{
   static class Element implements Comparable
   {
      // data members
      int id;   // object identifier
      double d; // profit density

      // constructor
      private Element(int theID, double theDensity)
      {
         id = theID;
         d = theDensity;
      }

     // method of Comparable
     /** return true iff this < x */
     public int compareTo(Object x)
     {
        double xD = ((Element) x).d;
        if (d < xD)
           return -1;
        if (d == xD)
           return 0;
        return 1;
      }
  
      /** return true iff this == x */
      public boolean equals(Object x)
         {return d == ((Element) x).d;}
   }

   /** set x[i] = 1 iff object i included in knapsack, 1 <= i < p.length
     * param p[1:p.length-1] array of profits
     * param w[1:w.length-1] array of weights
     * param c knapsack capacity
     * return value of greedy knapsack filling */
   public static double greedyKnapsack(double [] p, double [] w, double c,
                                       int [] x)
   {
      // define an element array to be sorted by profit density
      Element [] q = new Element [p.length];
      for (int i = 1; i < p.length; i++)
         // array of profit densities
         q[i] = new Element(i, p[i] / w[i]);
   
      // sort by density
      HeapSort.heapSort(q);
   
      // load in nonincreasing order of density and compute profit sum
      double profitSum = 0;      // will be sum of profits
      for (int i = p.length - 1; i > 0; i--)
      {
         int id = q[i].id;
         if (w[id] <= c )
         {// object id fits
            x[id] = 1;
            c -= w[id];
            profitSum += p[id];
         }
         else // object id does not fit
            x[id] = 0;
      }
      return profitSum;
   }
}


The above code together with test data and output appear in the files GreedyKnapsack.*.