java - ArrayIndexOutOfBoundsException :0 occurs when trying to read in a file from the Linux command line in Java?

Question

所以我试图从 Linux 命令行接受一个文本文件到我的 Java 程序中，但是编译器给了我标题中提到的错误。它说错误发生在“String fileName = args[0];”这一行。有没有人碰巧知道为什么？这是我的代码:

public class Parsons_Decoder
{
  // method: main
  // purpose: receives key-phrase and sequence of integers and
  // prints the secret message to the screen.
  public static void main(String[] args) throws IOException
  {
    String fileName = args[0];

    // reads incoming file (if it exists) and saves the key-phrase to
    // String variable "keyPhrase"
    File testFile = new File(fileName);

    if(!testFile.exists())
    {
      System.out.println("\nThis file does not exist.\n");
      System.exit(0);
    }

    Scanner inputFile = new Scanner(args[0]);
    String keyPhrase = inputFile.nextLine();

    // creates an ArrayList and stores the sequence of integers into it
    ArrayList<Integer> numArray = new ArrayList<Integer>();

    while(inputFile.hasNextInt())
    {
      numArray.add(inputFile.nextInt());
    }

    // decodes and prints the secret message to the screen
    System.out.println();
    System.out.print("Your secret message is: ");

    for(int i = 0; i < numArray.size(); i++)
    { 
      int num = numArray.get(i);
      System.out.print(keyPhrase.charAt(num));
    }
    System.out.println("\n");

    //keyboard.close();
    inputFile.close();
  }
}

Answer 1

更新:

你的教授要求你使用标准输入读入一个文件，使用如下命令:

java Diaz_Decoder < secretText1.txt

您的 main() 方法应该如下所示:

public static void main(String[] args) throws IOException {
    // create a scanner using stdin
    Scanner sc = new Scanner(System.in);

    String keyPhrase = inputFile.nextLine();

    // creates an ArrayList and stores the sequence of integers into it
    ArrayList<Integer> numArray = new ArrayList<Integer>();

    while (inputFile.hasNextInt()) {
        numArray.add(inputFile.nextInt());
    }

    // decodes and prints the secret message to the screen
    System.out.println();
    System.out.print("Your secret message is: ");

    for (int i = 0; i < numArray.size(); i++) {
        int num = numArray.get(i);
        System.out.print(keyPhrase.charAt(num));
    }

    System.out.println("\n");
}