Unable to convert arraylist of type string to arralist integer and pass the new list to a method

Question

public class PGM2 { public static void main (String [] args){ try { Scanner scn = new Scanner(new File("/D:filename")); scn.useDelimiter("/n"); ArrayList<String> Stringarraylist = new ArrayList<String>(); while (scn.hasNext()){ Stringarraylist.add((scn.next())); } ArrayList<Integer> numbers = new ArrayList<Integer>(); for (String s : Stringarraylist){ numbers.add (Integer.parseInt(s)); } //numbers.add((Stringarraylist.get(i))); System.out.println("the given list is :"+ numbers); scn.close();`enter code here` } catch (Exception e) { System.out.println("the exception found is "+ e); } } }

My input file has some values I intend to use them later in the program. I have used an ArrayList to collect all those values but unable to store them directly into the ArrayList<Integer> hence tried to type cast but NumberNotFound exception is coming.

Well that mean your try to parse a String that does not represent a number. — Jean-François Savard
– Jean-François Savard, Commented Feb 2, 2015 at 21:07
What are the contents of your file? Also, if you are trying to split by lines, the delimiter /n is incorrect, you should be using \n. Also the Scanner class has a function called 'hasNextInt()` and nextInt() methods you should look into. — Vincent McNabb
– Vincent McNabb, Commented Feb 2, 2015 at 21:09
Have you tried printing out the Strings without parsing to verify that you're trying to parse the right thing? — merlin2011
– merlin2011, Commented Feb 2, 2015 at 21:12
Change your statement for printing the exception to print e.getMessage() - it will often provide a more helpful message about what is going wrong. — sprinter
– sprinter, Commented Feb 2, 2015 at 21:20

Beri · Accepted Answer · 2015-02-03 07:10:08Z

This will work.

variable names start from small letter.
you need to use /r and /n for new lines - it depends is you are using windows or linux.

Here is the working code:

 public static void main(String[] args) { Pattern p = Pattern.compile("-?[0-9]+"); try { Scanner scn = new Scanner(new File("C:/workspace/test.txt")); scn.useDelimiter("[\\r\\n]+"); ArrayList<Integer> numbers = new ArrayList<Integer>(); while (scn.hasNext()) { String s = scn.next().trim(); if (p.matcher(s).matches()) { // this will skip invalid lines numbers.add(Integer.parseInt(s)); } } System.out.println("the given list is :" + numbers); scn.close(); } catch (Exception e) { System.out.println("the exception found is " + e); } }

And second solution, using better Scanner class. Scanner can find integers for you.

 public static void main(String[] args) { try { Scanner scn = new Scanner(new File("C:/workspace/test.txt")); ArrayList<Integer> numbers = new ArrayList<Integer>(); while (scn.hasNext()) { if(scn.hasNextInt()){ numbers.add(scn.nextInt()); } } System.out.println("the given list is :" + numbers); scn.close(); } catch (Exception e) { System.out.println("the exception found is " + e); } } }

Hi thanks for the reply ..but my input file has some negative integers as well ..will this work fine ?
for (int k =0; k < Stringarraylist.size();k++){ int temp = Integer.parseInt(Stringarraylist.get(k)); System.out.println("the input just passed is :"+temp);

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