Question

所以我有一个任务，我们必须使用Sieve of Eratosthenes算法生成0之间的所有素数，用户确定的值小于200，然后将这些素数写入一个名为“primesTo200.txt”的文件中，最大值每行10个素数。现在，当我输入120作为最大素数值时，我的代码工作得很好，但是当我尝试输入0到200之间的任何其他数字时，它会生成素数很好但是当它尝试时我得到一个“越界异常”错误写入文件。这是为什么？？我没有硬编码任何只会使120个工作的东西......有人可以帮助我吗？ ^ _ ^

import java.util.Arrays;
import java.util.Scanner;
import java.io.*;

public class A1Q1
{
  public static void main(String[] args)
  {
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Enter a maximum value up to which you wish to generate prime numbers [max 200]: ");
    int maxValue = keyboard.nextInt();

    while(maxValue > 200 || maxValue < 0)
    {
      System.out.println("Sorry, that is not a max value between [0 - 200]. Please enter another integer: ");
      maxValue = keyboard.nextInt();
    }

    int[] primes = generatePrimes(maxValue);
    System.out.println(Arrays.toString(primes));

    try
    {
      FileWriter fileName = new FileWriter("primesTo200.txt.");
      recordArray(primes, fileName);
    }

    catch(IOException ioe)
    {
      ioe.printStackTrace();
    }
  }


  public static int[] generatePrimes(int maxValue)
  {
    boolean[] array = new boolean[maxValue + 1];
    int[] primesFull = new int[maxValue];
    int count = 0;

    for(int i = 2; i < array.length; i++)
    {
      array[i] = true;
    }

    for(int nextPrime = 2; nextPrime * nextPrime <= maxValue; nextPrime++)
    {
      for(int i = 2; i * nextPrime <= maxValue; i++)
      {
        array[i * nextPrime] = false;
      }
    }

    for(int i = 2; i <= maxValue; i++)
    {
      if(array[i] == true)
      {
        primesFull[count] = i;
        count++;
      }
    }

    int[] primes = new int[count];
    System.arraycopy(primesFull, 0, primes, 0, count);

    return primes;
  }


  public static void recordArray(int[] primes, FileWriter fileName)
  {
    PrintWriter fileOut = new PrintWriter(fileName);
    int lineLength = 10;
    int count = 0;

    while(count < primes.length)
    {
      for(int i = 0; i < lineLength; i++)
      {
        fileOut.print(primes[count] + " ");
        count++;
      }
      fileOut.print("\n");
    }

    fileOut.close();
    System.out.println("Program wrote to the file successfully.");
  }
}

Answer 1

for(int i = 0; i < lineLength; i++)就是问题所在。

每次你的外循环迭代（并跳过count < primes.length的检查）时，你将经历10个素数，无论你是否有10个素数留在你的文件中

编程Eratosthenes的Sieve并写入文件

1 个答案: