Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.
162
Chapter 7 Generating the Server Response: HTTP Response Headers
Listing 7.4  Primes.java (continued)
      start = start.add(TWO);
    if (start.isProbablePrime(ERR_VAL))
      return(start);
    else
      return(nextPrime(start));
  }
  private static boolean isEven(BigInteger n) {
    return(n.mod(TWO).equals(ZERO));
  }
  private static StringBuffer[] digits =
    { new StringBuffer("0"), new StringBuffer("1"),
      new StringBuffer("2"), new StringBuffer("3"),
      new StringBuffer("4"), new StringBuffer("5"),
      new StringBuffer("6"), new StringBuffer("7"),
      new StringBuffer("8"), new StringBuffer("9") };
  private static StringBuffer randomDigit() {
    int index = (int)Math.floor(Math.random() * 10);
    return(digits[index]);
  }
  public static BigInteger random(int numDigits) {
    StringBuffer s = new StringBuffer("");
    for(int i=0; i
      s.append(randomDigit());
    }
    return(new BigInteger(s.toString()));
  }
  /** Simple command line program to test. Enter number
   *  of digits, and it picks a random number of that
   *  length and then prints the first 50 prime numbers
   *  above that.
   */
  
  public static void main(String[] args) {
    int numDigits;
    if (args.length > 0)
      numDigits = Integer.parseInt(args[0]);
    else
      numDigits = 150;
    BigInteger start = random(numDigits);
    for(int i=0; i<50; i++) {
      start = nextPrime(start);
      System.out.println("Prime " + i + " = " + start);
    }
  }
}
Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.
Servlet and JSP training courses by book's author: courses.coreservlets.com.






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