How can I modify this Java program to read in the names from a file designated in the command line?

Question

Right now I have this program set up to where I can input names of boats in the command line i.e. C:\java Proj3 "Boat 1" "Boat 2" "Boat 3" and it prints the results to the command line based on the specs. Instead, I want to type something like this in the command line C:\java Proj3 "C:\class\Java\boatnames.txt" "C:\class\Java\results.txt" so the args come from the file specified and the results are printed in a text file instead of on the screen. I changed the println's to printf's, but that's it so far. I deleted all my other failed attempts at this. I even tried creating another class called createfile.java that had private Formatter x; and some openFile, closeFile, and addRecords methods, but if I move the output over there and try to put it in addRecords, it doesn't know what the variable i is, and I'm guessing there must be a simpler way where I don't have to create that createfile class.

Here is my code(I didn't include the other classes since all I need to do is replace the args from the command line with args from a txt file in the command line):

import java.util.*;
import java.io.*;
import java.lang.*;
import java.swing.*;

public class Proj3 {
    public static void main(String args[]) {

            Boat[] Boats;
        char   firstChar;
        char   secondChar;
        int    i;    

        Boats = new Boat[args.length];

        for (i = 0; i < args.length; i++) {

            firstChar = args[i].toUpperCase().charAt(0);
            secondChar = args[i].toUpperCase().charAt(1);

            if ((firstChar == 'B') || (firstChar == 'C') || (firstChar ==     'N')) {
                Boats[i] = new SailBoat();
            } else {
                Boats[i] = new RaceBoat();
            }

            Boats[i].setName(args[i]);

            if ((secondChar == 'A') || (secondChar == 'E')) {
            Boats[i].goFast();
            } else {
                Boats[i].goSlow();
            }
        }


        for (i = 0; i < args.length; i++) {
            System.out.printf("Boat number " + (i + 1) + " - \n");
            System.out.printf("   ");
            Boats[i].printBoat();
            System.out.printf("   ");
            Boats[i].whatIsBoatState();
        }




    }
}

While you're waiting, you could have a quick glance of Basic I/O. I'd pay particular attention to the Buffered Streams personally — MadProgrammer
– MadProgrammer, Commented Sep 25, 2012 at 1:36

Bohemian · Accepted Answer · 2012-09-25 01:47:43Z

3

The simplest way is to use an existing library to read the file in. A very-commonly used library is apache commons-io, which has the FileUtils.readLines() utility method.

import org.apache.commons.io.FileUtils;

// pass the filename is to your program on the command line

List<Sting> lines = FileUtils.readLines(new File(args[0]));
for (String line : lines) {
    // use "line" instead of args[i] in your current code
    ...
}

answered Sep 25, 2012 at 1:47

Bohemian♦

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1 Comment

KevinPaul Over a year ago

This looks like the best answer since you are replacing args. It's due in 5 hours, and I just download the apache stuff, so hopefully I'll figure out what to do after that. Thank you.

Ted Hopp · Accepted Answer · 2012-09-25 01:52:46Z

3

Right now, the top-level program logic is contained in one monolithic main() method. To make life easier, you should break it down into logical pieces and implement each piece in a separate method. For instance, your main() method might look something like this:

public static void main(String[] args) {
    ArrayList<Boat> boats = getBoats(args[0]);
    PrintStream out = getOutputStream(args[1]);
    printBoats(boats, out);
    out.close();
}

Then you need to write the support routines:

private ArrayList<Boat> getBoats(String inputFileName) {
    ...
}
PrintStream getOutputStream(String outputFileName) {
    ...
}
void printBoats(ArrayList<Boat> boats, PrintStream output) {
    ...
}

You will probably have to make it all a little more complicated to deal with I/O exceptions (missing files, write permissions, etc.). You'll also have to modify the methods Boat.printBoat() and Boat.whatIsBoatState() to take a PrintStream argument.

answered Sep 25, 2012 at 1:52

Ted Hopp

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3 Comments

KevinPaul Over a year ago

I appreciate the help, but I'm not supposed to change the program that much. I'm simply supposed to modify the program above to simply take the args from a file instead of the command line, so that the rest of the program runs the same way it did. You did show me a new way to do it though, so thank you for helping me learn that.

Ted Hopp Over a year ago

@IQtheMC - "runs the same way" can mean many things. Reorganizing the code (sometimes drastically) while keeping the same behavior is called "code refactoring". It is an essential skill for programmers to learn, and it's never too early to start. :)

KevinPaul Over a year ago

Agreed. I still have a lot to learn. Thank you very much for taking the time to help.

Community · Accepted Answer · 2017-05-23 11:56:17Z

1

follow this

java-Passing argument into main method

obtain the files base don absolute path and obtain the file object then read the file object to pickup the content.

edited May 23, 2017 at 11:56

CommunityBot

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answered Sep 25, 2012 at 1:42

Sanath

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Comments

MadProgrammer · Accepted Answer · 2012-09-25 01:52:57Z

I've not tested this, but I've not tested it any great detail

public static void main(String[] args) {

    if (args.length == 2) {

        String inFileName = args[0];
        String outFileName = args[1];

        File inFile = new File(inFileName);
        if (inFile.exists()) {

            try {

                List<Boat> boats = new ArrayList<Boat>(25);

                // Read the "boats" file...
                BufferedReader br = null;
                try {

                    br = new BufferedReader(new FileReader(inFile));
                    String text = null;
                    while ((text = br.readLine()) != null) {

                        char firstChar = text.toUpperCase().charAt(0);
                        char secondChar = text.toUpperCase().charAt(1);

                        Boat boat = null;
                        if ((firstChar == 'B') || (firstChar == 'C') || (firstChar == 'N')) {
                            boat = new SailBoat();
                        } else {
                            boat = new RaceBoat();
                        }

                        boat.setName(text);

                        if ((secondChar == 'A') || (secondChar == 'E')) {
                            boat.goFast();
                        } else {
                            boat.goSlow();
                        }

                        boats.add(boat);

                    }

                } finally {
                    try {
                        br.close();
                    } catch (Exception e) {
                    }
                }

                BufferedWriter bw = null;
                try {

                    bw = new BufferedWriter(new FileWriter(outFileName, false));
                    for (int index = 0; index < boats.size(); index++) {

                        bw.write("Boat number " + (index + 1) + " - ");
                        bw.newLine();
                        bw.write("    " + boat.toString() + "    " + boat.getBoatState());

                    }

                    bw.flush();

                } finally {
                    try {
                        bw.close();
                    } catch (Exception e) {
                    }
                }

            } catch (IOException exp) {
                exp.printStackTrace();
            }

        }

    }

}

The other problem is, you're going to need to provide some additional functionality to your Boat class

Namely, I used boat.toString() which needs to return the value Boat.printBoat() was printing and boat.getBoatState() which needs to return the value that Boat.getBoatState() was printing

Thank you very much. This isn't exactly what I wanted, but again, I learned a lot from it. I really appreciate people taking the time out off their day to help others with these problems.

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