Our text discusses an Object-Oriented approach to finding prime numbers by means of the sieve of Eratosthenes. It's given in C++ in the text. Here's the equivalent program in Java. The program doesn't have any comments for documentation. We'll discuss it in class, and you can see the text for details.

SieveDemo.java

public class SieveDemo {
   public static void main (String [] args) {
      int colcounter=0;
   
      Counter c = new Counter(2);    // initialize the Counter c at 2
      Sieve s = new Sieve(c);       // initialize the Sieve s's source to c
      int next;
      do {
         next = s.out();            // get the next prime
         System.out.format("%5d ", next);  // and print it
         if ((++colcounter)%10==0)
           System.out.println();
      } while (next < 10000);   
      System.out.println();
   }
}

Item.java

public class Item {
   protected Item source;

   public Item () {}

   public Item (Item sourceIn) {
     source = sourceIn;
   }

   public int out() {
     return 0;
   }
}

Filter.java

public class Filter extends Item {
   private int factor;

   public Filter (Item sourceIn, int factorIn) {
      source = sourceIn;
      factor = factorIn;
   }

   public int out() {
      int n;
      do
         n = source.out();
      while (n % factor == 0);
      return n;
   }
}

Counter.java

public class Counter extends Item {
   private int value;

   public Counter (int valueIn) {
     value = valueIn;
   }

   public int out() {
     return value++;
   }
}

Sieve.java

public class Sieve extends Item {
   private int value;

   public Sieve (Item sourceIn) {
     source = sourceIn;
   }

   public int out() {
     int n = source.out();
     source = new Filter(source,n);
     return n;
   }
}

Here's the beginning of a run of the program:

$ java SieveDemo
    2     3     5     7    11    13    17    19    23    29
   31    37    41    43    47    53    59    61    67    71

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