Effectively use the String, Character, and StringBuilder classes and associated

Question

Effectively use the String, Character, and StringBuilder classes and associated methods
Write Java code to read and write data to and from a file
Deliverables:

Design, develop, test and document a Java application that reads data from an input file, processes the data, and then writes the processed data to an output file

Specific functional requirements for this project:

The application should be run from the command line using command line arguments to provide the input and output filenames.
//The application should display an appropriate error message if the user forgets to enter the input and output filenames at the command prompt or if the files are not found.
//The application should open the file and read each line of the file.
//For each line read, the application should determine the total number of characters in the line (including white-space characters), determine the number of times the number 4 appears in the line, replace all occurrences of the string "this" with "That", and reverse the order of the characters in the line.
//The output file should contain the same number of lines as the input file with the following content for each line:
//Total number of characters (including white-space characters) in the line
//Number of times the number 4 appeared in the line
//Reversed string (for example, cats in the input file would be displayed as stac)
//The items on each line in the output file should be separated by commas (for example: for input line "this4cats", the output line should be "9,1,stac4tahT")
//
//6.The application should close any open files before exiting.

Explanation / Answer

public class JFile {

public static void main(String[] args) throws IOException {

if( args.length != 2 ){

System.out.println("Invalid no of Args:");

System.out.println("Usage: JFile <input file> <output file>");

return;

}

BufferedReader br = null;

BufferedWriter bw = null;

try {

String path = System.getProperty("user.dir");

br = new BufferedReader(new FileReader( path + "\"+ args[0]));

bw = new BufferedWriter(new FileWriter( path + "\" +args[1]) );

} catch (IOException e) {

System.out.println( "Unable to open file: " + e.toString());

return;

}

String line;

while( (line = br.readLine()) !=null){

int Cnt4=0;

line = line.replaceAll("this", "That");

for( int i=0; i<line.length(); i++)

if( Character.isDigit(line.charAt(i)) )

if ( line.charAt(i) == '4')

Cnt4++;

StringBuilder s = new StringBuilder();

s.append(line);

s.reverse();

s.insert(0, Cnt4 + ", ");

s.insert(0, line.length() + ", ");

bw.write(s.toString() + " ");

System.out.println(s.toString());

}

try {

if (br != null)br.close();

if( bw!=null ) bw.close();

} catch (IOException ex) {

ex.printStackTrace();

}

}

}

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