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7.3 Persistent Servlet State and Auto Reloading Pages

161

Listing 7.3  PrimeList.java (continued)

  public synchronized Vector getPrimes() {

    if (isDone())

      return(primesFound);

    else

      return((Vector)primesFound.clone());

  }

  public int numDigits() {

    return(numDigits);

  }

  public int numPrimes() {

    return(numPrimes);

  }

  public synchronized int numCalculatedPrimes() {

    return(primesFound.size());

  }

}

Listing 7.4  Primes.java 

package coreservlets;

import java.math.BigInteger;

/** A few utilities to generate a large random BigInteger,

 *  and find the next prime number above a given BigInteger.

*/

public class Primes {

  // Note that BigInteger.ZERO was new in JDK 1.2, and 1.1

  // code is being used to support the most servlet engines.

  private static final BigInteger ZERO = new BigInteger("0");

  private static final BigInteger ONE = new BigInteger("1");

  private static final BigInteger TWO = new BigInteger("2");

  // Likelihood of false prime is less than 1/2^ERR_VAL

  // Assumedly BigInteger uses the Miller Rabin test or

  // equivalent, and thus is NOT fooled by Carmichael numbers.

  // See section 33.8 of Cormen et al's Introduction to

  // Algorithms for details.

  private static final int ERR_VAL = 100;

  public static BigInteger nextPrime(BigInteger start) {

    if (isEven(start))

      start = start.add(ONE);

    else

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