Can someone check my codes about replacing numbers in a .txt file? I can't replace the numbers in it

Question

I have the following code, which is for an assignment to replace numbers in a text file:

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Random;
import java.util.Scanner;

public class L20 {

   public static void main(String[] args) throws IOException {
      Scanner input = new Scanner(System.in);

      System.out.println("Enter file name");
      String in = input.nextLine();
      try {
         textWriter(in);
         textReader(in);
         textChanger(in);
      } catch (Exception e) {
      }
   }

   public static void textWriter(String path) throws IOException {
      String[] alphabet = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j",
            "k", "m", "l", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w",
            "x", "y", "z" };
      File file = new File(path);
      Writer output = null;
      Random number = new Random();
      output = new BufferedWriter(new FileWriter(file));
      int lines = 10 + number.nextInt(11);
      for (int i = 0; i < lines; i++) {
         int it2 = 1 + number.nextInt(9);
         int n1 = number.nextInt(26);
         int n2 = number.nextInt(26);
         int n3 = number.nextInt(26);

         String t2 = Integer.toString(it2);
         String t1 = alphabet[n1] + alphabet[n2] + alphabet[n3];
         String text = t1 + t2;
         output.write(text);
         ((BufferedWriter) output).newLine();
      }
      output.close();
      System.out.println("Your file has been written");
   }

   public static void textReader(String path) throws IOException {
      File file = new File(path);
      Scanner input;
      input = new Scanner(file);
      String line;
      while ((line = input.nextLine()) != null) {
         System.out.println(line);
      }
      input.close();
   }
}

But unfortunately the code isn't working as it should. The problem portion is shown below:

public static void textChanger(String path) throws IOException {
   File file = new File(path);

   Scanner input;
   input = new Scanner(file);
   String line;
   Pattern p = Pattern.compile("[0-9]");

   while ((line = input.nextLine()) != null) {
      Matcher m = p.matcher(line);
      int n = Integer.parseInt(m.group());
      System.out.println(n);
   }

   input.close();
}

What I want to do is replace only the number part of each line in the Text.txt file. Each of these lines consists of three letters and one number. I only want to change the number portion.

Answer 1

Try this.............

public class Reg {

    public static void main(String[] args){

        String s = "abc1";
        Pattern p = Pattern.compile("\\d");
        Matcher m = p.matcher(s);
        String no = new String();

        while (m.find()){

              no = m.group();
        }

        String newStr = s.replace(no, "hi");
        System.out.println(newStr);
       }
}