Master/Reference Architectures and Patterns/hjp5/examples/PrimeNumberTools.java


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/* PrimeNumberTools.java */

public class PrimeNumberTools
{
  public void printPrimeFactors(int num)
  {
    int whichprime = 1;
    int prime;
    String prefix;

    prefix = "primeFactors("+num+")= ";
    while (num > 1) {
      prime = getPrime(whichprime);
      if (num % prime == 0) {
        System.out.print(prefix+prime);
        prefix = " ";
        num /= prime;
      } else {
        ++whichprime;
      }
    }
    System.out.println();
  }

  public int getPrime(int cnt)
  {
    int i = 1;
    int ret = 2;

    while (i < cnt) {
      ++ret;
      if (isPrime(ret)) {
        ++i;
      }
    }
    return ret;
  }

  private boolean isPrime(int num)
  {
    for (int i = 2; i < num; ++i) {
      if (num % i == 0) {
        return false;
      }
    }
    return true;
  }
}