使用扫描仪类（java）更改文本文件中的特定文本

Question

I write this code that can search for the some specific text (such as word) in the text file with scanner class, but i want also to replace (old text to the new text) in the same old text locuation. i find in the internet that i must used replaceAll method like ( replaceAll(old, new); ) but it does't work with the scanner class.

This is my code, it just search (if it existed ) write new text in new line without change the old one.

Do i need to change the method (to get the data) form scanner to FileReader ??

File file = new File("C:\\Users....file.txt");
Scanner input = new Scanner(System.in);
System.out.println("Enter the content you want to change:");
String Uinput = input.nextLine();
System.out.println("You want to change it to:");
String Uinput2 = input.nextLine();

Scanner scanner = new Scanner(file).useDelimiter(",");
BufferedWriter writer  = new BufferedWriter(new FileWriter(file, true));
while (scanner.hasNextLine()) {
    String lineFromFile = scanner.next();
    if (lineFromFile.contains(Uinput)) {
        lineFromFile = Uinput2;
        writer.write(lineFromFile); 
        writer.close();
        System.out.println("changed " + Uinput + " tO " + Uinput2);
        break;
    }
    else if (!lineFromFile.contains(Uinput)){
        System.out.println("Don't found " + Uinput);
        break;
    }
}

Answer 1

You cannot read from a file, then write to that same file. You need 2 different files.

  while (read line from input file) { 
      if (NOT matches your search pattern)
            write line to output file.
      else  { // matches
          write start of line to your search pattern.
          write your replace string
          write from end of search pattern to end of line.
      }
   }

Unless your replace string is the same size as your search string, yes, you'll have to use 2 files. Consider the file:

 Blah
 Blah
 Blah

Now replace the letter 'a' with "The quick Brown Fox". If you replace the first line, you've overwritten the rest of the file. Now you can't read the 2nd line, so YES, you'll have to use 2 files.

Answer 2

Here's another answer based on @Sedrick comment and your code. I'm adding it to your pseudo code.

File file = new File("C:\\Users....file.txt");
Scanner input = new Scanner(System.in);
System.out.println("Enter the content you want to change:");
String Uinput = input.nextLine();
System.out.println("You want to change it to:");
String Uinput2 = input.nextLine();

Scanner scanner = new Scanner(file).useDelimiter(",");
java.util.List<String> tempStorage = new ArrayList<>();

while (scanner.hasNextLine()) {
    String lineFromFile = scanner.next();
    tempStorage.add(lineFromFile);
}

 // close input file here
// Open your write file here (same file = overwrite).

// now loop through temp storage searching for input string.
for (String currentLine : tempStorage ) {
     if (!lcurrentLine.contains(Uinput)){
        String temp = currentLine.replace(Uinput, Uinput2);
         write a line using temp variable  
     } else { // not replaced
         write a line using currentLine;  
 }
 // close write file here

By the way, you'll have to encase the reads writes with try catch to trap for IOExceptions. That's how I knew it was pseudo code. There are plenty of examples for reading/writing a file on this web site. It's easy to search for.