如何从命令行作为参数输入的文本文件中读取逗号分隔的字符串？

Question

I am writing a program that sorts hospital records. These records come in a text file that the user inputs in the command-line as an argument when they call the class "Patient" that is below. The format of the records for each line in the text file is lastname(string), firstname(string), roomnumber(int),age(int). The number of lines is unknown. The user will specify the file name as the first argument and then specify the field on which to sort. What I am specifically having trouble figuring out is how to read in the text file and store the information in an array. I have been stuck on it for about a week so far so I have started from scratch a few times. Here is what I have so far.

import java.util.*;
import java.io.*;

public class Patient
{
        public static void main(String args[])
    {
        System.out.println("Servando Hernandez");
        System.out.println("Patient sorting Program.");

        Scanner scan = new Scanner(args[0]);
        String[] Rec = new String[10];
        while(scan.hasNextLine)
        {

          scan.nextLine = Rec[i];


        }
        Arrays.sort(Rec);
        for(int j=0; j<Rec.length; j++)
        {
            System.out.println(Rec[j]);
        }
    }
}

Answer 1

The number of lines is unknown

This would suggest you need a dynamic data structure which can grow to meet your needs. Consider using some kind of List

List<String> lines = new ArrayList<>(10);
while(scan.hasNextLine)
{
    lines.add(scan.nextLine());
}

Have a look at Collections Trail for more details

Because you're dealing with structured data, I'd consider creating POJO of some kind to make it easier to manage...

public class PatientRecord {
    private final String firstName;
    private final String lastName;
    private final int roomNumber;
    private final int age;

    public PatientRecord(String firstName, String lastName, int roomNumber, int age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.roomNumber = roomNumber;
        this.age = age;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public int getRoomNumber() {
        return roomNumber;
    }

    public int getAge() {
        return age;
    }


}

Then, when you read the line from the file, you would parse it, creating a new instance of PatientRecord and add this to your List instead.

This means that you can then use things like Collections.sort to sort the List based on your needs

Answer 2

Now, I'm not too sure that this is exactly what you want, because they code you gave me isn't much, but here is your same code, fixed, slightly refactored, and set to return the lines as they are read in, but sorted by last name:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;


public class Patient {

    public static void main(String args[]) {
        System.out.println("Servando Hernandez");
        System.out.println("Patient sorting Program.");

        Scanner scan = null;
        try {
            scan = new Scanner(new File(args[0]));
        } catch (FileNotFoundException e) {
            System.err.println("File path \"" + args[0] + "\" not found.");
            System.exit(0);
        }

        ArrayList<String> lines=new ArrayList<String>();
        while(scan.hasNextLine())
            lines.add(scan.nextLine());

        Collections.sort(lines);

        for(String x : lines)
            System.out.println(x);
    }
}

I hope this helps, and best of luck to you.