Getting input inside a loop using Java

Question

I'm trying to use scanner.nextLine() inside a loop, but I get an exception. The problem is located in this part of the code.

        while(!sentence.equals("quit")){
        dealWithSentence(sentence, voc);
        System.out.println("Enter your sentence:");
        sentence = scanner.nextLine();
    }

There is the exception:

Exception in thread "main" java.util.NoSuchElementException: No line found at java.util.Scanner.nextLine(Unknown Source) at il.ac.tau.cs.sw1.ex4.SpellingCorrector.main(SpellingCorrector.java:34)

That's my full method code:

    public static void main(String[] args) throws Exception{
    Scanner scanner = new Scanner(System.in);
    String filePath = scanner.nextLine();
    if (filePath.contains(" ")){
        scanner.close();
        throw new Exception("[ERROR] the file path isnt correct");
    }

    File file = new File(filePath);
    String[] voc = scanVocabulary(new Scanner(file));
    if (voc == null)
    {
        scanner.close();
        throw new Exception("[ERROR] the file isnt working");

    }


    System.out.println("Read " + voc.length + " words from " + file.getName());

    System.out.println("Enter your sentence:");

    String sentence = scanner.nextLine();

    while(!sentence.equals("quit")){
        dealWithSentence(sentence, voc);
        System.out.println("Enter your sentence:");
        sentence = scanner.nextLine();
    }
    scanner.close();

Kulvinder Singh · Accepted Answer · 2015-11-13 08:54:00Z

Scanner.nextLine() works as follows..

   String s = "Hello World! \n 3 + 3.0 = 6.0 true ";

   // create a new scanner with the specified String Object
   Scanner scanner = new Scanner(s);

   // print the next line
   System.out.println("" + scanner.nextLine());

   // print the next line again
   System.out.println("" + scanner.nextLine());

   // close the scanner
   scanner.close();
   }

this will give you the following output

Hello World!
3 + 3.0 = 6.0 true

So basically it starts scanning and skips until the first new line character, and then it returns whatever it has skipped so far as the output. In your case if you have only a single sentence and no new line (\n) in it at all, it will skip the entire length and never find a new line. thereby throwing the exception... add a new line character in mid of sentence and see if the exception goes away

Credits go to : http://www.tutorialspoint.com/java/util/scanner_nextline.htm

user1438038 · Accepted Answer · 2015-11-13 08:55:59Z

2

Check scanner.hasNextLine() before you use scanner.nextLine():

if (scanner.hasNextLine()) {
  sentence = scanner.nextLine();
}

Otherwise, the scanner might not have any element and cannot provide a next line.

Usually, you will read your input in a loop, such as:

while (scanner.hasNextLine()) {
  System.out.println("Line: " + scanner.nextLine());
}

answered Nov 13, 2015 at 8:55

user1438038

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5 Comments

Kulvinder Singh Over a year ago

Op, This is better. Use this.

user5153746 Over a year ago

but the problem is there is no next line, I want to get it as an input from the user

user1438038 Over a year ago

You'll have to loop over the input steam then and each time a line is terminated, the Scanner will return a nextLine().

user5153746 Over a year ago

you mean each loop needs to contain Scanner sc = new Scanner(System.in);? because I've tried it but it doesnt work as well

user1438038 Over a year ago

No, just create one Scanner instance and make it read user input in a loop. To prevent the NoSuchElementException, check your scanner with hasNext() before calling nextLine().

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