Editing text files

Question

Im trying to write a program that opens many files .def and should replace every / with \.
but I'm encountering problem with the method that has to replace the character in the file.
first attempt:
public void changer(String pathFile){
     try{
          RandomAccessFile toEdit = new RandomAccessFile(new File(pathFile), "rw");
          String line = "";
          while(line != null){
               riga = toEdit.readLine();
               String newLine;
               newLine = line.replaceAll("/", "\\");
               toEdit.writeChars(newLine);
          toEdit.close();
     catch(IOException e){
          System.out.println(e.getMessage);
          System.exit(1);
}this throws an exception java.lang.StringIndexOutOfBoundException: String index out of range: 1
exception in thrown by replaceAll method.
second attempt:
public void changer(String pathFile){
     try{
          RandomAccessFile toEdit = new RandomAccessFile(new File(pathFile), "rw");
          String line = "";
          while(line != null){
               riga = toEdit.readLine();
               String newLine;
               for(int i = 0; i<line.length(); i++){
                    if(riga.charAt(i) == '/'){
                         newLine = line.replace('/', '\\')
                         toEdit.writeChars(nuovaRiga)
                    else
                         continue;
          toEdit.close();
     catch(IOException e){
          System.out.println(e.getMessage);
          System.exit(1);
}this throws an exception java.lang.NullPointerException
thrown by length() method.
problem 2: both method don't replace line with newLine but just write newLine after line in the text.
I've read the api documentation for RandomAccessFile but I haven't found a method that really substitute the line or only the char.
any suggestion?

Answer 1

No, you are never reading a second line, you read into riga, which you ignore.oh, sorry, that was an error in copying/translating my code.
here's the correct one.
public void changer(String pathFile){
     try{
          RandomAccessFile toEdit = new RandomAccessFile(new File(pathFile), "rw");
          String line = "";
          while(line != null){
               line = toEdit.readLine();
               String newLine;
               newLine = line.replaceAll("/", "\\");
               toEdit.writeChars(newLine);
          toEdit.close();
     catch(IOException e){
          System.out.println(e.getMessage);
          System.exit(1);
public void changer(String pathFile){
     try{
          RandomAccessFile toEdit = new RandomAccessFile(new File(pathFile), "rw");
          String line = "";
          while(line != null){
               line = toEdit.readLine();
               String newLine;
               for(int i = 0; i<line.length(); i++){
                    if(line.charAt(i) == '/'){
                         newLine = line.replace('/', '\\')
                         toEdit.writeChars(newLine);
                    else
                         continue;
          toEdit.close();
     catch(IOException e){
          System.out.println(e.getMessage);
          System.exit(1);
}