Question

I’ve been doing a small project for class, it runs perfectly without problems but when pitted against the class’s auto testers it gives back 2 No line found errors. Asking the course’s staff they say it’s probably because I’m trying to scan a line when none exist, but I tried printing all my scans and didn’t discover anything like that.
That’s all the scans I have in my code:

Scanner sc = new Scanner(System.in);
    String sentence;
    int choice;

    System.out.println("Please enter a sentence:");
    sentence = sc.nextLine();

    printMenu(); // calls a function to print the menu.

    // gets the require action
    System.out.println("Choose option to execute:");
    choice = sc.nextInt();
    sc.nextLine();

(I tried with and without the last sc.nextLine)

static void replaceStr(String str)
{
    String oldWord, newWord;
    Scanner in = new Scanner(System.in);

    // get the strings
    System.out.println("String to replace: ");
    oldWord = in.nextLine();
    System.out.println("New String: ");
    newWord = in.nextLine();

    // replace
    str = str.replace(oldWord, newWord);
    System.out.println("The result is: " + str);
    in.close();
}
static void removeNextChars(String str)
{
    Scanner in = new Scanner(System.in);
    String remStr; // to store the string to replace
    String tmpStr = ""; //the string we are going to change.
    int i; // to store the location of indexStr

    // gets the index
    System.out.println("Enter a string: ");
    remStr = in.nextLine();
    i=str.indexOf(remStr);

    in.close(); // bye bye

    if (i < 0)
    {
        System.out.println("The result is: "+str);
        return;
    }

    // Build the new string without the unwanted chars.
    /* code that builds new string */

    str = tmpStr;
    System.out.println("The result is: "+str);
}

Any idea how a line can leak here?

Answer 1

Here is the problem. You are using in.close(); at multiple places(last statement in replaceStr method and around the middle in removeNextChars method). When you close the scnaner using close() method, it closes your InputStream (System.in) as well. That InputStream can’t be reopened with-in your program.

public void close() throws IOException --> Closes this input stream and releases any system resources associated with this stream. The general contract of close is that it closes the input stream. A closed stream cannot perform input operations and **cannot be reopened.**

Any read attempts after the scanner close will result into exception NoSuchElementException.

Please close your scanner only once, when your program is done.

EDIT: Scanner Closing/usage:

In yout main function:

   Scanner sc = new Scanner(System.in);
   ....
   .....
   replaceStr(Scanner sc, String str);
   .....
   ....
   removeNextChars(Scanner sc ,String str);
   ....
   ....
   //In the end
   sc.close();


static void replaceStr(Scanner in, String str){
  //All the code without scanner instantiation and closing
  ...
}

static void removeNextChars(Scanner in, String str){
  //All the code without scanner instantiation and closing
  ...
}

You should be all good.