// LineNumberer.java
// Add line numbers to each line in a file 

import java.io.*;  // import classes for file I/O
import java.util.Scanner;

public class LineNumberer {
  
  public static void main(String[] args) {
    
    String inputFileName, outputFileName, currLine, numberedLine;
    Scanner in = new Scanner(System.in);  // for keyboard input
    Scanner fileIn = null;                // for file input
    PrintWriter fileOut = null;           // for file output
    
    // get input file name
    System.out.print("Enter input file name: ");
    inputFileName = in.next();
    
    // get output file name
    System.out.print("Enter output file name: ");
    outputFileName = in.next();

    try {
      // important: use these to read from and write to files
      fileIn = new Scanner(new File(inputFileName));
      fileOut = new PrintWriter(new FileWriter(outputFileName));
      
      // read each line, prepend current line number, and write out
      int count = 0;
      while (fileIn.hasNextLine()) {
        currLine = fileIn.nextLine();
        count++;
        numberedLine = count + ": " + currLine;
        fileOut.println(numberedLine);     // write numbered line to file
        System.out.println(numberedLine);  // print numbered line to screen
      }
    } 
    catch (IOException e) {
      System.out.println("Error: " + e.getMessage());
    } 
    finally {
    // close files
      if (fileIn != null)
        fileIn.close();
      if (fileOut != null)
        fileOut.close();
    }
  }
}