Question

How can I read an existing text file and modify some of its value based on some condition like if I get some text like

Apple 1 3 5

Now, here whenever I get an integer value I have to increase its count by 1 and save back to the same file again.

For example, if I read some content like above I should be able to save

Apple 2 4 6

back to the same file again

My code looks like

try{
FileWriter fstream = new FileWriter(“c:\Apple.txt”,true);

        FileReader inputFileReader   = new FileReader("c:\\Apple.txt");
        BufferedReader inputStream   = new BufferedReader(inputFileReader);
        PrintWriter    outputStream  = new PrintWriter(fstream);



        while((inline=inputStream.readLine())!=null)
        {
            values=inline.split("-");

            Integer l = Integer.parseInt(values[2])+1;
            outputStream.print((inline.replaceAll(values[2],l.toString())));

        }

        outputStream.close();


    }

So, I get an output like

Apple 1 3 5 Apple 1 4 5

But my required output is

Apple 1 4 5

Thanks in advace

Answer 1

You can’t do it interactively on the same file (or at least maybe you can but it would be really tricky).. you could

• open the input file
• open the output file
• for each line in file
  • check your condition, if true
    • generate the new line according to what you are going to modify
    • save it on output file
  • if false
    • copy the line into new file without modifying it
• close both files
• delete first one and rename second one to first (you can do it easily with API functions)