Java Replace Line In Text File

Question

How do I replace a line of text found within a text file   I have a string such as   Do the dishes0   And I want to update it with   Do the dishes1    and vise versa   How do I accomplish this   ActionListener al   new ActionListener                      Override                 public void actionPerformed ActionEvent e                        JCheckBox checkbox    JCheckBox  e getSource                        if  checkbox isSelected                              System out println  Selected                            String s   checkbox getText                            replaceSelected s   1                          else                           System out println  Deselected                            String s   checkbox getText                            replaceSelected s   0                                                            public static void replaceSelected String replaceWith  String type         By the way  I want to replace ONLY the line that was read   NOT the entire file

User · Answer

Since Java 7 this is very easy and intuitive to do.

List<String> fileContent = new ArrayList<>(Files.readAllLines(FILE_PATH, StandardCharsets.UTF_8));

for (int i = 0; i < fileContent.size(); i++) {
    if (fileContent.get(i).equals("old line")) {
        fileContent.set(i, "new line");
        break;
    }
}

Files.write(FILE_PATH, fileContent, StandardCharsets.UTF_8);

Basically you read the whole file to a List, edit the list and finally write the list back to file.

FILE_PATH represents the Path of the file.

User · Answer

If replacement is of different length    Read file until you find the string you want to replace  Read into memory the part after text you want to replace  all of it  Truncate the file at start of the part you want to replace  Write replacement  Write rest of the file from step 2    If replacement is of same length    Read file until you find the string you want to replace  Set file position to start of the part you want to replace  Write replacement  overwriting part of file    This is the best you can get  with constraints of your question  However  at least the example in question is replacing string of same length  So the second way should work   Also be aware  Java strings are Unicode text  while text files are bytes with some encoding  If encoding is UTF8  and your text is not Latin1  or plain 7-bit ASCII   you have to check length of encoded byte array  not length of Java string

User · Answer

Well you would need to get a file with JFileChooser and then read through the lines of the file using a scanner and the hasNext   function  http   docs oracle com javase 7 docs api javax swing JFileChooser html  once you do that you can save the line into a variable and manipulate the contents

User · Answer

I was going to answer this question  Then I saw it get marked as a duplicate of this question  after I d written the code  so I am going to post my solution here   Keeping in mind that you have to re-write the text file  First I read the entire file  and store it in a string  Then I store each line as a index of a string array  ex line one   array index 0  I then edit the index corresponding to the line that you wish to edit  Once this is done I concatenate all the strings in the array into a single string  Then I write the new string into the file  which writes over the old content  Don t worry about losing your old content as it has been written again with the edit  below is the code I used   public class App    public static void main String   args         String file    file txt       String newLineContent    Hello my name is bob       int lineToBeEdited   3       ChangeLineInFile changeFile   new ChangeLineInFile        changeFile changeALineInATextFile file  newLineContent  lineToBeEdited             And the class   import java io BufferedWriter  import java io File  import java io FileNotFoundException  import java io FileOutputStream  import java io FileReader  import java io IOException  import java io OutputStreamWriter  import java io UnsupportedEncodingException  import java io Writer   public class ChangeLineInFile    public void changeALineInATextFile String fileName  String newLine  int lineNumber            String content   new String            String editedContent   new String            content   readFile fileName           editedContent   editLineInContent content  newLine  lineNumber           writeToFile fileName  editedContent           private static int numberOfLinesInFile String content        int numberOfLines   0      int index   0      int lastIndex   0       lastIndex   content length   - 1       while  true             if  content charAt index       n                 numberOfLines                        if  index    lastIndex                numberOfLines   numberOfLines   1              break                    index                return numberOfLines     private static String   turnFileIntoArrayOfStrings String content  int lines        String   array   new String lines       int index   0      int tempInt   0      int startIndext   0      int lastIndex   content length   - 1       while  true             if  content charAt index       n                 tempInt                 String temp2   new String                for  int i   0  i  lt  index - startIndext  i                      temp2    content charAt startIndext   i                             startIndext   index              array tempInt - 1    temp2                      if  index    lastIndex                 tempInt                 String temp2   new String                for  int i   0  i  lt  index - startIndext   1  i                      temp2    content charAt startIndext   i                             array tempInt - 1    temp2               break                    index                return array     private static String editLineInContent String content  String newLine  int line         int lineNumber   0      lineNumber   numberOfLinesInFile content        String   lines   new String lineNumber       lines   turnFileIntoArrayOfStrings content  lineNumber        if  line    1            lines line - 1      n    newLine        else           lines line - 1    newLine            content   new String         for  int i   0  i  lt  lineNumber  i              content    lines i              return content     private static void writeToFile String file  String content         try  Writer writer   new BufferedWriter new OutputStreamWriter new FileOutputStream file    utf-8               writer write content         catch  UnsupportedEncodingException e               TODO Auto-generated catch block         e printStackTrace          catch  FileNotFoundException e               TODO Auto-generated catch block         e printStackTrace          catch  IOException e               TODO Auto-generated catch block         e printStackTrace             private static String readFile String filename        String content   null      File file   new File filename       FileReader reader   null      try           reader   new FileReader file           char   chars   new char  int  file length             reader read chars           content   new String chars           reader close          catch  IOException e            e printStackTrace          finally           if  reader    null                try                   reader close                  catch  IOException e                       TODO Auto-generated catch block                 e printStackTrace                                      return content

User · Answer

just how to replace strings    as i do first arg will be filename second target string third one the string to be replaced instead of targe  public class ReplaceString        public static void main String   args throws Exception           if args length lt 3 System exit 0           String targetStr   args 1           String altStr   args 2           java io File file   new java io File args 0            java util Scanner scanner   new java util Scanner file           StringBuilder buffer   new StringBuilder            while scanner hasNext               buffer append scanner nextLine   replaceAll targetStr  altStr              if scanner hasNext   buffer append   n                      scanner close            java io PrintWriter printer   new java io PrintWriter file           printer print buffer           printer close

User · Answer

At the bottom  I have a general solution to replace lines in a file  But first  here is the answer to the specific question at hand  Helper function   public static void replaceSelected String replaceWith  String type        try              input the file content to the StringBuffer  input          BufferedReader file   new BufferedReader new FileReader  notes txt             StringBuffer inputBuffer   new StringBuffer            String line           while   line   file readLine       null                inputBuffer append line               inputBuffer append   n                      file close            String inputStr   inputBuffer toString             System out println inputStr      display the original file for debugging             logic to replace lines in the string  could use regex here to be generic          if  type equals  0                  inputStr   inputStr replace replaceWith    1   replaceWith    0               else if  type equals  1                  inputStr   inputStr replace replaceWith    0   replaceWith    1                          display the new file for debugging         System out println  ---------------------------------- n    inputStr               write the new string with the replaced line OVER the same file         FileOutputStream fileOut   new FileOutputStream  notes txt            fileOut write inputStr getBytes             fileOut close           catch  Exception e            System out println  Problem reading file               Then call it   public static void main String   args        replaceSelected  Do the dishes    1             Original Text File Content      Do the dishes0      Feed the dog0   Cleaned my room1   Output      Do the dishes0    Feed the dog0    Cleaned my room1    ----------------------------------   Do the dishes1   Feed the dog0   Cleaned my room1   New text file content      Do the dishes1   Feed the dog0   Cleaned my room1     And as a note  if the text file was      Do the dishes1   Feed the dog0   Cleaned my room1   and you used the method replaceSelected  Do the dishes    1     it would just not change the file     Since this question is pretty specific  I ll add a more general solution here for future readers  based on the title       read file one line at a time    replace line as you read the file and store updated lines in StringBuffer    overwrite the file with the new lines public static void replaceLines         try              input the  modified  file content to the StringBuffer  input          BufferedReader file   new BufferedReader new FileReader  notes txt             StringBuffer inputBuffer   new StringBuffer            String line           while   line   file readLine       null                line          replace the line here             inputBuffer append line               inputBuffer append   n                      file close                write the new string with the replaced line OVER the same file         FileOutputStream fileOut   new FileOutputStream  notes txt            fileOut write inputBuffer toString   getBytes             fileOut close           catch  Exception e            System out println  Problem reading file

[java] Java Replace Line In Text File

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