exercise5_6.java

Introduction to java programming 一书中所有编程练习部分的源码

public class Exercise5_6 {
  /** Main method */
  public static void main(String[] args) {
    final int NUM_OF_PRIMES = 50;
    // Store prime numbers
    int[] primeNumbers = new int[NUM_OF_PRIMES];
    int count = 0; // Count the number of prime numbers
    int number = 2; // A number to be tested for primeness
    boolean isPrime = true; // Is the current number prime?

    System.out.println("The first 50 prime numbers are \n");

    // Repeatedly find prime numbers
    while (count < NUM_OF_PRIMES) {
      // Assume the number is prime
      isPrime = true;

      // Test if number is prime
      for (int i = 0; i < count &&
        primeNumbers[i] <= Math.sqrt(number); i++) {
        //If true, the number is not prime
        if (number % primeNumbers[i] == 0) {
          // Set isPrime to false, if the number is not prime
          isPrime = false;
          break; // Exit the for loop
        }
      }

      // Print the prime number and increase the count
      if (isPrime) {
        primeNumbers[count] = number;
        count++; // Increase the count

        if (count % 10 == 0) {
          // Print the number and advance to the new line
          System.out.println(number);
        }
        else
          System.out.print(number + "\t");
      }

      // Check if the next number is prime
      number++;
    }
  }
}