CODEWITHSUNDEEP
javaarraysindexoutofboundsexception
user2872194
user2872194

Reputation: 147

Using elements of 2 arrays to populate a 3rd. Out of bounds error

I have to read a text file and make the first number of each line a size of an array. Then I had to populate a 3rd array with the first two arrays. No matter what I try I always get the contents of the first array into the 3rd array, but I get an out of bounds exception going to the 2nd. What am I doing wrong?

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

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

        File file = new File("twoLists.txt");

        try
        {

            Scanner read = new Scanner(file);

            int size = read.nextInt();
            //array 1 size and population
            int list1[] = new int[size];

            for (int i = 0; i < list1.length; i++)
            {
                list1[i] = read.nextInt();
            }

            //array2 size and population
            int size2 = read.nextInt();
            int list2[] = new int[size2];

            for (int i = 0; i < list2.length; i++)
            {
                list2[i] = read.nextInt();
            }

            //combine the arrays
            int list3[] = new int[list1.length + list2.length];
            for (int i = 0; i < list3.length; i++)
            {

                //if i is < the length of list 1 populate the array
                //with contents of list
                if (i < list1.length)
                {
                    list3[i] = list1[i];
                }
                if (i > list1.length)
                {
                    list3[i] = list2[i];
                }
            }

        }
        catch (FileNotFoundException e)
        {
            e.printStackTrace();
        }

    }
}

Upvotes: 0

Views: 60

Answers (3)

niceman
niceman

Reputation: 2673

use this code instead :

int j=0;
for (int i = 0; i < list3.length; i++)
{
  //if i is < the length of list 1 populate the array
  //with contents of list
  if (i < list1.length)
  {
     list3[i] = list1[i];
  }
  if (i > list1.length)
  {
    list3[i] = list2[j++];
  }
}

you're using the same index for list3 and list2 which are very different in size(list3 is list2 and list1 combined), if you don't like defining a new variable try this:

for (int i = 0; i < list3.length; i++)
{
  //if i is < the length of list 1 populate the array
  //with contents of list
  if (i < list1.length)
  {
     list3[i] = list1[i];
  }
  if (i > list1.length)
  {
    list3[i] = list2[i-list1.length];
  }
}

you can also seperate it into two for loops and defining i outside the loop,after all the compiler will loop over list3 whether one loop or two loops.

Upvotes: 1

msrd0
msrd0

Reputation: 8390

Your mistake is here:

if (i > list1.length)
{
    list3[i] = list2[i];
}

You say that i must be greater than list1.length, but require the value of i - change it to this to make it work:

if (i > list1.length)
{
    list3[i] = list2[i-list1.length];
}

Upvotes: 3

chiastic-security
chiastic-security

Reputation: 20520

Your problem is here:

if (i > list1.length)
{
     list3[i] = list2[i];
}

You're correctly indexing list3, but you're acting as if the indexing of list2 carried on from where list1 left off. It doesn't: it starts from 0, just like all arrays.

Try

if (i > list1.length)
{
     list3[i] = list2[i-list1.length];
}

and that should sort things out.

Upvotes: 2

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