// Fig. I.10: BitSetTest.java
// Using a BitSet to demonstrate the Sieve of Eratosthenes.
import java.util.BitSet;
import java.util.Scanner;

public class BitSetTest 
{
   public static void main( String args[] )
   {
      // get input integer
      Scanner scanner = new Scanner( System.in );
      System.out.println( "Please enter an integer from 2 to 1023" );
      int input = scanner.nextInt();

      // perform Sieve of Eratosthenes
      BitSet sieve = new BitSet( 1024 );
      int size = sieve.size(); 

      // set all bits from 2 to 1023
      for ( int i = 2; i < size; i++ )
         sieve.set( i );

      // perform Sieve of Eratosthenes
      int finalBit = ( int ) Math.sqrt( size );

      for ( int i = 2; i < finalBit; i++ ) 
      {
         if ( sieve.get( i ) ) 
         {
            for ( int j = 2 * i; j < size; j += i ) 
               sieve.clear( j );
         } // end if
      } // end for

      int counter = 0; 

      // display prime numbers from 2 to 1023
      for ( int i = 2; i < size; i++ )
      {
         if ( sieve.get( i ) ) 
         {
            System.out.print( String.valueOf( i ) );
            System.out.print( ++counter % 7 == 0 ? "\n" : "\t" );
         } // end if
      } // end for

      // display result
      if ( sieve.get( input ) )
         System.out.printf( "\n%d is a prime number", input );
      else
         System.out.printf( "\n%d is not a prime number", input );
   } // end main
} // end class BitSetTest

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