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();
        }




    }
}

Answer 1

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

Answer 2

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.

Answer 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
    ...
}

Answer 4

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.