How to open a txt file and read numbers in Java

Question

How can I open a  txt file and read numbers separated by enters or spaces into an array list

User · Accepted Answer

Read file  parse each line into an integer and store into a list   List lt Integer gt  list   new ArrayList lt Integer gt     File file   new File  file txt    BufferedReader reader   null   try       reader   new BufferedReader new FileReader file        String text   null       while   text   reader readLine       null            list add Integer parseInt text            catch  FileNotFoundException e        e printStackTrace      catch  IOException e        e printStackTrace      finally       try           if  reader    null                reader close                    catch  IOException e               print out the list System out println list

User · Answer

try       BufferedReader br   new BufferedReader new FileReader  textfile txt         String strLine        Read File Line By Line     while   strLine   br readLine       null               Print the content on the console       System out println  strLine               Close the input stream     in close         catch  Exception e    Catch exception if any       System err println  Error      e getMessage          finally       in close            This will read line by line   If your no  are saperated by newline char  then in place of    System out println  strLine     You can have   try  int i   Integer parseInt strLine    catch NumberFormatException npe     do something       If it is separated by spaces then    try      String noInStringArr     strLine split         then you can parse it to Int as above      catch NumberFormatException npe         do something

User · Answer

A much shorter alternative is below   Path filePath   Paths get  file txt    Scanner scanner   new Scanner filePath   List lt Integer gt  integers   new ArrayList lt  gt     while  scanner hasNext          if  scanner hasNextInt              integers add scanner nextInt           else           scanner next              A Scanner breaks its input into tokens using a delimiter pattern  which by default matches whitespace  Although default delimiter is whitespace  it successfully found all integers separated by new line character

User · Answer

File file   new File  file txt       Scanner scanner   new Scanner file   List lt Integer gt  integers   new ArrayList lt  gt     while  scanner hasNext          if  scanner hasNextInt              integers add scanner nextInt                else           scanner next            System out println integers

User · Answer

import java io      public class DataStreamExample          public static void main String args                   try                  FileWriter  fin new FileWriter  testout txt                    BufferedWriter d   new BufferedWriter fin               int a     new int 3               a 0  1              a 1  22              a 2  3              String s                 for int i 0 i lt 3 i                                  s Integer toString a i                    d write s                   d newLine                               System out println  Success                d close                fin close                       FileReader in new FileReader  testout txt                BufferedReader br new BufferedReader in               String i                 int sum 0              while   i br readLine      null                                sum    Integer parseInt i                             System out println sum              catch Exception e  System out println e                                     OUTPUT   Success 26  Also  I used array to make it simple     you can directly take integer input and convert it into string and send it to file  input-convert-Write-Process    its that simple

User · Answer

Good news in Java 8 we can do it in one line   List lt Integer gt  ints   Files lines Paths get fileName                              map Integer  parseInt                             collect Collectors toList

[java] How to open a txt file and read numbers in Java

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