Reading a file and changing one part of the file

Question

I am trying to read a file and then I want to change the first value on each line. The file I am reading is a .HEADER file. Which is just read in notepad I am just opening this like a txt file. I get no say at all how this file is created originally
I want to change the value on the first line the a new title plus the ext .dat. The file is below. This stays the same format just with different values.
ECG000 1 171 26112 9:14:56 23/04/2002
ECG000 8 43(0) 8 127 79 -24066 0 AED trace
I want to change the ECG000 to a new value eg Pat1.dat on the first line and Pat1 on the second line. When I read this file in and output to the dos window I get ECG000 0 0 0 and that is it. Any ideas why this is happening and how I can replace the values in the file??
     private void FileExt() throws IOException
          System.out.println("In function");
          BufferedReader br = new BufferedReader(new FileReader("c:\\Projects\\FirstSupport\\ECG000.HEADER"));
          String s;
          Vector data = new Vector();
          ECGFile = new FileWriter("c:\\Projects\\FirstSupport\\ECG.txt",true);
          System.out.println("Reading the file");
          while ((s = br.readLine()) != null)
          data.add(s);
          System.out.println(s);
          System.out.println("Finished");
          String label = s.substring(0, s.indexOf(" "));
          System.out.println(label);
          String newLabel = (label+".dat");
          System.out.println(newLabel);
     }

Answer 1

I think this is what you're looking for:     private void FileExt() {
          java.util.List data=new ArrayList();
          String s;
          try {
               BufferedReader br=new BufferedReader(new InputStreamReader(
                    new FileInputStream(new File("ECG000.HEADER"))));
               while ((s = br.readLine()) != null)  {
                    data.add(s);
                    System.out.println(s);
               br.close();
          catch (FileNotFoundException fnfe) {
               System.out.println("Input file not found");
               return;
          catch (IOException ioe) {
               ioe.printStackTrace();
               return;
          ListIterator li=data.listIterator();
          try {
               PrintWriter ECGFile=new PrintWriter(new FileOutputStream(
                    new File("ECG.txt")));
               while(li.hasNext()) {
                    s=(String)li.next();
                    if (s.substring(0, 6).equals("ECG000")) {
                         s="Pat1.dat"+s.substring(6, s.length());
                    ECGFile.println(s);
               ECGFile.close();
          catch (FileNotFoundException fnfe1) {}
     }Mark