Error using Substring : String Index out of range : -1 Java

Question

In this program I am just getting input from a file and trying to get the boys name and the girls name out of it, and also put them in separate files. I have done everything just as the book has stated. And I've also searched everywhere online for help with this but cant seem to find anyone with the same problem. Ive seen problems where its not -1 but a positive number because they went to far out of the string calling a substring over the strings length. But cant seem to figure out this giving me -1 since i's value is 1.

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


public class Homework_11_1 {

public static void main(String[] args)throws FileNotFoundException 
{
   File inputFile = new File("babynames.txt");
   Scanner in = new Scanner(inputFile);
   PrintWriter outBoys = new PrintWriter("boys.txt");
   PrintWriter outGirls = new PrintWriter("girls.txt");


   while (in.hasNextLine()){
    String line = in.nextLine();
    int i = 0;
    int b = 0;
    int g = 0;
    while(!Character.isWhitespace(line.charAt(i))){ i++; }
    while(Character.isLetter(line.charAt(b))){ b++; }
    while(Character.isLetter(line.charAt(g))){ g++; }
    String rank = line.substring(i);
    String boysNames = line.substring(i, b);
    String girlsNames = line.substring(b, g);
    outBoys.println(boysNames);
    outGirls.println(girlsNames);
    }

    in.close();
    outBoys.close();
    outGirls.close();
    System.out.println("Done");
}


}

Here is the txt file

    1 Jacob Sophia
    2 Mason Emma
    3 Ethan Isabella
    4 Noah Olivia
    5 William Ava
    6 Liam Emily
    7 Jayden Abigail
    8 Michael Mia
    9 Alexander Madison
    10 Aiden Elizabeth

To increase i, you will need while(Character.isWhitespace... instead of while(!Character.isWhitespace... — C.B.
– C.B., Commented May 1, 2014 at 21:23
That's probably because b and g are never increased. Add System.out.println(b); etc to see whats happening. Or better yet - use a debugger. — C.B.
– C.B., Commented May 1, 2014 at 21:27
Use system.out.print statements in your loops to see how your code reacts. — ObedMarsh
– ObedMarsh, Commented May 1, 2014 at 21:32

Jakkra · Accepted Answer · 2014-05-01 21:32:49Z

1

I would have written it an other way, using split.

public static void main(String[] args)throws FileNotFoundException 
    {
       File inputFile = new File("babynames.txt");
       Scanner in = new Scanner(inputFile);
       PrintWriter outBoys = new PrintWriter("boys.txt");
       PrintWriter outGirls = new PrintWriter("girls.txt");


       while (in.hasNextLine()){
        String line = in.nextLine();
        String[] names = line.split(" "); // wile give you [nbr][boyName][GirlName]

        String boysNames = names[1];
        String girlsNames = names[2];
        outBoys.println(boysNames);
        outGirls.println(girlsNames);
        }

        in.close();
        outBoys.close();
        outGirls.close();
        System.out.println("Done");
    }

answered May 1, 2014 at 21:32

Jakkra

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1 Comment

NathanH Over a year ago

Thanks for showing me this. Helped me better understand using the split method! Got some good notes on it now.

mattarod · Accepted Answer · 2014-05-01 21:32:21Z

0

Rather than fuss with loops and substring(), I'd just use String.split(" "). Of course, the assignment may not permit you to do this.

But anyway, without giving you the answer to the assignment, I can tell you that your logic is wrong. Walk through it and find out why. If you try running this code on just the first line of the input file, you'll get these values: i=1, b=0, and g=0. Calling line.substring(1,0) is obviously not going to work.

answered May 1, 2014 at 21:32

mattarod

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1 Comment

NathanH Over a year ago

Thanks for all the help, I ended up figuring it out. I guess I was just not in the right mind set at the time!

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