Java while(input.hasnextline) loop not exiting?

Question

SO I'm supposed to determine the number of lines in a text file (a 100 lines containg numbers) and then create an array with the the number of lines, but the first while loop used to find out the number of lines in the text file never exits. The second loop which is the exacts same one works just fine. Please help me out!

static void main(String[] args) throws Exception{
    java.io.File file = new java.io.File("seriesOfNumbers.txt"); //file instance                
    Scanner input = new Scanner(file); //Scanner
    int M =0 ;
    while (input.hasNextLine() && !input.equals(null))// ** Loop never exits, tried almost everything
    {
        k++;
    }
    double[] numberArray = new double[k];
    int V = 0;
    while (input.hasNextLine())// When I exit the first loop this one exits just fine
    {
        numberArray[j] = (double) input.nextInt();
        j++;
    }

You never advance the Scanner, you should call one of its .next* methods. — Daniël Knippers
– Daniël Knippers, Commented Mar 24, 2014 at 10:50
be careful with input.equals(null). if input is really null, you will get NullPointerException. use input != null instead — Baby
– Baby, Commented Mar 24, 2014 at 10:54
@user3454973 If an answer has solved your question, then please mark the answer as accepted. — skiwi
– skiwi, Commented Mar 24, 2014 at 14:45

skiwi · Accepted Answer · 2014-03-24 10:50:47Z

1

You are never consuming your input in the first loop, do that with input.nextLine().

You are now looping until input.hasNextLine() becomes false, but that never happens, because you do not consume the input.

answered Mar 24, 2014 at 10:50

skiwi

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Comments

Shriram · Accepted Answer · 2014-03-24 10:52:01Z

0

Use input.next() to move to next line. In While condition you are checking the has next line and not null. Thats y it is in infinite loop.

answered Mar 24, 2014 at 10:52

Shriram

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Vinay Veluri · Accepted Answer · 2014-03-24 10:53:20Z

0

In this below code, this is initialising

Scanner input = new Scanner(file); //Scanner

This is reading

int M =0 ;
while (input.hasNextLine() && !input.equals(null))
{
    input.nextLine();  // Use this to advance the lines from scanner
    k++;
}

answered Mar 24, 2014 at 10:53

Vinay Veluri

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Comments

Alexander Jardim · Accepted Answer · 2014-03-24 11:00:38Z

0

It seems to me that you could use FileUtils class from apache.commons.io project to do the trick.

static void main(String[] args) throws Exception{
    List<String> lines = FileUtils.readLines(new File("..."));

Now, if you really need the numberArray for some other computation, you can

    double[] d = new double[lines.size()];

Or you can use the Collection to iterate

    for (String line : lines) {
        double n = Double.parseDouble(line);

To use FileUtils, take a look at http://commons.apache.org/proper/commons-io/

But, iof all that you want is to know what is wrong with your code, you should call the method Scanner.nextLine() inside your first while loop.

answered Mar 24, 2014 at 11:00

Alexander Jardim

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Comments

Angela Amarapala · Accepted Answer · 2018-10-04 10:12:18Z

0

In order to stop the infinite looping of the while loop even after consuming the required inputs, we can use a break statement.

Here is an example,

    while (scanner.hasNextLine()) {
            String[] arr = scanner.nextLine().split(" ");
            long[] ar = new long[n];
            for (int i = 0; i < n; i++) {
                ar[i] = Long.parseLong(arr[i]);
            }
            long result = sum(ar);
            System.out.println(result);
            break;
        }

answered Oct 4, 2018 at 10:12

Angela Amarapala

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