Question

4.3Learning Objective: To read and write text files.

Instructions: This is complete program with one Java source code file named H01_43.java (your main class is named H01_43).

Problem: Write a program that prompts the user for the name of a Java source code file (you may assume the file contains Java source code and has a .java filename extension; we will not test your program on non-Java source code files). The program shall read the source code file and output the contents to a new file named the same as the input file, but with a .txt file name extension, e.g., if the input file is foo.java then the output file shall be named foo.java.txt. Each line of the input file shall be numbered with a line number (formatted as shown below) in the output file. For example, if the user enters H01_43.java as the name of the input file and H01_43.java contains:

//***************************************************************

// CLASS: H01_43

//***************************************************************

public class H01_43 {

public static void main(String[] pArgs) {

}

private run() {

}

}

then the contents of the output file H01_43.java.txt would be:

[001] //***************************************************************

[002] // CLASS: H01_43

[003] //***************************************************************

[004] public class H01_43 {

[005] public static void main(String[] pArgs) {

[006] }

[007] private run() {

[008] }

[009] }

You may assume that the file being read exists.

Hint: To print an integer as shown above in a field of width 3 with leading 0's use the Java API PrintWriter.printf() method with a format specifier of %03d. The % symbol tells the compiler this is a format specifier, 3 is the field width for the integer line number, the 0 preceding 3 tells the compiler to output leading 0's rather than leading spaces if the line number does not take up the entire field width, and d tells the compiler that we are printing an integer).

Testing: Make sure to test the case where the input file exists but is empty.

Answer 1

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.PrintWriter;
import java.util.Scanner;

public class CopyFile {
   public static void main(String[] args) throws Exception {
       Scanner sc = new Scanner(System.in);
       System.out.println("Enter file name");
       String name = sc.nextLine();
       BufferedReader br = null;
       try {
           br = new BufferedReader(new FileReader(name));
       } catch (FileNotFoundException e) {
           e.printStackTrace();
           return;
       }
       String line = br.readLine();
       int lineCount = 1;
       PrintWriter pw = new PrintWriter(new FileWriter(name + ".txt"));
       while (line != null) {
           pw.printf("[%03d]", lineCount++);
           pw.println(line);
           line=br.readLine();
       }
       pw.flush();
       pw.close();
       br.close();

   }
}