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Friday, 19 August 2016

Chapter 5 Exercise 20, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

*5.20 (Display prime numbers between 2 and 1,000) Modify Listing 5.15 to display all the prime numbers between 2 and 1,000, inclusive. Display eight prime numbers per line. Numbers are separated by exactly one space.

public class ProgrammingEx5_20 {
  public static void main(String[] args) {
    final int UPPER_BOUND = 1000; // Upper bound
    final int NUMBER_OF_PRIMES_PER_LINE = 8; // Display 10 per line
    int count = 0; // Count the number of prime numbers
    int number = 2; // A number to be tested for primeness
 
    System.out.println("The prime numbers in from 2 to 1000 are");
 
    // Repeatedly find prime numbers
    while (number <= UPPER_BOUND) {
      // Assume the number is prime
      boolean isPrime = true; // Is the current number prime?
 
      // Test if number is prime
      for (int divisor = 2; divisor <= number / 2; divisor++) {
        if (number % divisor == 0) { // If true, number is not prime
          isPrime = false; // Set isPrime to false          
          break; // Exit the for loop
        }
      }
 
      // Print the prime number and increase the count
      if (isPrime) {
        count++; // Increase the count
 
        if (count % NUMBER_OF_PRIMES_PER_LINE == 0) {
          // Print the number and advance to the new line
          System.out.println(number);
        }
        else
          System.out.print(number + " ");
      }
 
      // Check if the next number is prime
      number++;
    }
  }
}

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