Write a program that reads an input file then print the input file data to an ou

Question

Write a program that reads an input file then print the input file data to an output file but with the following additions

1. each line in the outpfile is prefixed with the current line number, first line with 1. Second line with 2. etc

2. all empty lines or lines containing all blanks are not to be written to the output file

3. The program must not throw a FileNotFoundException, rather it should catch the exception in the program and ask the user again for a new input file name. Keep repeating until no exception is generated from opening the file to read and write.

Sample run if file Lab.java does not exist and Lab4.java exists

Please enter input file name: Lab.java

Please enter outputfile name: Lab.out

File does not exist

Please enter input file name: Lab4.java

Please enter outputfile name: Lab.out

Input File :

public class Lab4

{

public static void main(String[] args) throws FileNotFoundException

{

String a = "c3.txt";

String x = "xyz.txt";

File b = new File(a);

Scanner in = new Scanner(b);

Scanner key = new Scanner(System.in);

String data = "";

while (in.hasNextLine())

{

data += in.nextLine();

}

String d = key.next();

d = key.next();

d = d + data;

System.out.println(d);

}

}

Output file

1.public class Lab

2.{

3.  public static void main(String[] args) throws FileNotFoundException

4.   {

5.    String a = "c3.txt";

6.   String x = "xyz.txt";

7.   File b = new File(a);

8.   Scanner in = new Scanner(b);

9.   Scanner key = new Scanner(System.in);

10.   String data = "";

11.   while (in.hasNextLine())

12.   {

13.   data += in.nextLine();

14.   }

15.   String d = key.next();

16.   d = key.next();

17.   d = d + data;

18.   System.out.println(d);

19.  

20.   }

21.}

Explanation / Answer

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class WriteNumberedFile {
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
while(true)
{
System.out.print("Please enter input file name: ");
String inputFile = sc.nextLine();
System.out.print("Please enter outputfile name: ");
String outputFileName = sc.nextLine();
System.out.println();
  
try {
FileReader fr = new FileReader(inputFile);
Scanner fileScanner = new Scanner(fr);
FileWriter fw = new FileWriter(outputFileName);
  
int count = 0;
while(fileScanner.hasNextLine())
{
String line = fileScanner.nextLine();
if (line.trim().length() > 0)
{
fw.write(count + "." + line + " ");
count++;
}
}
fw.close();
fileScanner.close();
fr.close();
break;
} catch (FileNotFoundException e) {
System.out.println("File does not exist");
}
catch(IOException e)
{
System.out.println("Unable to write to file.");
}
}
sc.close();
}
}

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