Modify a specific content of a file with user defined value

Question

This is my current output:

********MENU********
1. UNIT
2. EXIT
*********************
Select your option from 1 or 2: 1
********MENU********
1. VIEW LIST
2. BACK TO MAIN
*********************
Select your option from 1 or 2: 1

This are the list of the units:
[1] Asero/California
[2] Captain America/Pennsylvania
What unit do you want to modify? 1
Asero/California
Asero/California
Unit Name: Iron Man
Unit Location: California
Return to menu? Select 1: 1
********MENU********
1. VIEW LIST
2. BACK TO MAIN
*********************
Select your option from 1 or 2: 1

This are the list of the units:
[1] Asero/California
[2] Captain America/Pennsylvania
What unit do you want to modify? 
Process interrupted by user.

What I wanted is the "Asero/California" is modified and replaced into "Iron Man/California".

The original output is still:

[1] Asero/California
[2] Captain America/Pennsylvania

My desired output is when I modify the data it should now be:

[1] Iron Man/California
[2] Captain America/Pennsylvania

I have a textfile = "practice.txt", which is where the data is stored.

I also have another text file = "tempPractice.txt", which is used just for putting a temporary data.

public class Practice
{
    List<String> lines = new ArrayList<String>();

    public Practice()
    {
        try
        {
            String line = "";
            System.out.println("********MENU********");
            System.out.println("1. UNIT");
            System.out.println("2. EXIT");
            System.out.println("*********************");
            System.out.print("Select your option from 1 or 2: ");

            Scanner sc = new Scanner(System.in);
            line = sc.next();

            if(line.equals("1"))
            {
                unitMenu();
            }
            else if(line.equals("2"))
            {
                System.exit(0);
            }
            else
            {
                System.out.println("Incorrect code, please select from 1 or 2.");
                new Practice();
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

    public void unitMenu()
    {
        try
        {
            String line = "";
            System.out.println("********MENU********");
            System.out.println("1. VIEW LIST");
            System.out.println("2. BACK TO MAIN");
            System.out.println("*********************");
            System.out.print("Select your option from 1 or 2: ");

            Scanner sc = new Scanner(System.in);
            line = sc.next();

            if(line.equals("1"))
            {
                updateData();
            }
            else if(line.equals("2"))
            {
                new Practice();
            }
            else
            {
                System.out.println("Incorrect code, please select from 1 or 2.");
                unitMenu();
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

    public void updateData()
    {
        lines = new ArrayList<String>();

        File f = new File("practice.txt");
        BufferedReader bR, bR2;
        BufferedWriter bW;
        Scanner sc, sc2;
        String str = "", scanLine, oldFile, newFile, tmpFile, uName, uLoc;
        int numLine;

        try
        {
            if(!f.exists())
            {
                System.out.println("File not found!");
            }
            else
            {
                bR = new BufferedReader(new FileReader("practice.txt"));
                while((str = bR.readLine()) != null)
                {
                    lines.add(str);
                }

                System.out.println();
                System.out.println("This are the list of the units:");
                for(int i=0,j=1;i<lines.size();i++,j++)
                {
                    System.out.println( "[" + j + "] " + lines.get(i).toString());
                }
                System.out.print("What unit do you want to modify? ");

                sc = new Scanner(System.in);
                numLine = sc.nextInt();

                int count = numLine;
                --count;

                for(int k=0;k<lines.size();k++)
                {                       
                    if(count == k)
                    {
                        System.out.println(lines.get(k).toString());

                        //used for checking to know what data it returns
                        oldFile = lines.get(count).toString();
                        System.out.println(oldFile);

                        //method to replace a data --> not working/trial and error?
                        bW = new BufferedWriter(new FileWriter("tmpPractice.txt"));
                        System.out.print("Unit Name: ");
                        sc = new Scanner(System.in);
                        uName = sc.nextLine();
                        bW.write(uName);
                        bW.append('/');
                        System.out.print("Unit Location: ");
                        sc2 = new Scanner(System.in);
                        uLoc = sc2.nextLine();
                        bW.write(uLoc);
                        bW.newLine();
                        bW.close();

                        System.out.print("Return to menu? Select 1: ");
                        sc = new Scanner(System.in);
                        scanLine = sc.next();
                        if(scanLine.equals("1"))
                        {
                            unitMenu();
                        }
                        else
                        {
                            System.out.println("Error. Select only 1.");
                            updateData();
                        }
                        bR2 = new BufferedReader(new FileReader("tmpPractice.txt"));
                        while((newFile = bR2.readLine()) != null)
                        {
                            tmpFile = newFile;
                            oldFile = tmpFile;

                            bW = new BufferedWriter(new FileWriter("practice.txt", true));
                            bW.write(oldFile);
                            bW.close();
                        }
                        System.out.println(oldFile);
                        bR2.close();
                    }
                    bR.close();
                }
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

    public static void main(String[] a)
    {
        new Practice();
    }
}

How would I do it? What should I do or what should I use in my code? Is there any simplier way to do this? Any feedback/suggestion/remarks/help would be deeply much appreciated.

I'm still new to Java, and I'm doing a lot of practice for myself, I reached up to the point where I can append a data to a file with IO, however, I still dont know how to modify/replace a specific data in the file without deleting all of its contents.

Please help me, I really want to learn more.

Answer 1

Take a look at this and modify accordingly.

    public static void replaceSelected(String address) {
            try {
                String x = "t";
                System.out.println("started searching for line");
        File inputFile1 = new File(old file where line is to be updated);
        File tempFile = new File(address+"/myTempFile.txt");


        BufferedReader reader = new BufferedReader(new FileReader(old file "));

        String lineToRemove = "add line to remove as a variable or a text";
        String currentLine;

        while((currentLine = reader.readLine()) != null) {
            // trim newline when comparing with lineToRemove
            String trimmedLine = currentLine.trim();
            if(trimmedLine.equals(lineToRemove) && x.contentEquals("t")) {
                x ="f";
            } else if(trimmedLine.equals(lineToRemove) && x.contentEquals("f")) {
                System.out.println("removed desired header");
                System.out.println("Line"+trimmedLine);
                continue;
            }
           FileWriter fw = new FileWriter(new file address,true);
                         BufferedWriter bw = new BufferedWriter(fw);
                         bw.write(currentLine);
                                         System.out.println(currentLine);
                          bw.write("\n");
                          bw.close();
        }
//        writer.close();
        reader.close();
         boolean success3 = (new File (old file address)).delete();
                            if (success3) {
                                System.out.println(" Xtra File deleted");

                            }
        } catch (Exception e){
}

Answer 2

I have worked out this code. In my code I have not used the temp file instead used the arraylist in to replace the old value with the new one.And After that I have write down the arraylist to the file. Please see below the changed code. I have only included the changed code here. This is working for me now.

            for(int k=0;k<lines.size();k++)
            {                       
                if(count == k)
                {
                    System.out.println(lines.get(k).toString());

                    //used for checking to know what data it returns
                    oldFile = lines.get(count).toString();
                    System.out.println(oldFile);

                    System.out.print("Unit Name: ");
                    sc = new Scanner(System.in);
                    uName = sc.nextLine();
                    System.out.print("Unit Location: ");
                    sc2 = new Scanner(System.in);
                    uLoc = sc2.nextLine();
                    String replaceString = uName+"/"+uLoc;
                    lines.set(k, replaceString);
                    FileOutputStream fop = null;
                    fop = new FileOutputStream(f);
                   for(String content:lines){
                       byte[] contentInBytes = content.getBytes();
                       fop.write(contentInBytes);
                       fop.write("\n".getBytes());
                   }

                   fop.flush();
                   fop.close();

                    System.out.print("Return to menu? Select 1: ");
                    sc = new Scanner(System.in);
                    scanLine = sc.next();
                    if(scanLine.equals("1"))
                    {
                        unitMenu();
                    }
                    else
                    {
                        System.out.println("Error. Select only 1.");
                        updateData();
                    }

                }
                bR.close();
            }

You used String replaceString = ...? Is the replaceString a value or a variable??

replaceString is a variable that contains the user enterd value to replace the desired string value in the file

Another is this: lines.set(k, replaceString) -> can I also declare this as public void replaceString??? or is this the easier way?

here we are replacing the indexed(k) value in the arraylist(lines) that contains the input file values, with the user enterd value.

And also, may I ask, what is the use of byte[], is it like charAt[] or more like Tokenizer?

now the replaced content is writing back to the file. For this we are converting the string value to the byte array(byte []) and writing using the FileOutputStream