NullPointerException and Array IO

Question

okay so I am a beginner at java and I am implementing a class which stores an array and sorts it using bubble sort.

import java.io.*;
public class Array
{
    private int array[];
    private int n;
    private BufferedReader br;
    public Array() throws IOException
    {
        System.out.print("Enter the size of the array : ");
        br=(new BufferedReader(new InputStreamReader(System.in)));
        n = Integer.parseInt(br.readLine());
        System.out.println("Enter "+ n +" integers");
        for(int i=0;i<n;i++)
        {

            array[i]=Integer.parseInt(br.readLine());
        }

    }
    public void showArray()
    {
        int i;
        for (i=0; i<n;i++)
        {
            System.out.print(array[i]+"  ");
        }
    }
    public void bubbleSort()
    {
        int max,last,i,j;
        last = n;
        for(i = 0; i<n ; i++)
        {
            max=0;
            for(j=0; j<last; j++)
            {
                max = (array[max]>array[j]) ? max : j ;

            }
            j = array[last];
            array[last] = array[max];
            array[max] = j;
            last--;
        }
    }
    public static void main(String [] args) throws IOException
    {
            Array a1 = new Array();
            System.out.println("Unsorted Array : ");
            a1.showArray();
            System.out.println("Sorted Array : ");
            a1.bubbleSort();
            a1.showArray();
    }
}

so when I run it it gives the error :

shubham@shubham-Inspiron-3542:~$ java Array
Enter the size of the array : 4
Enter 4 integers
11 9 7 16 4
Exception in thread "main" java.lang.NumberFormatException: For input string: "11 9 7 16 4"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at java.lang.Integer.parseInt(Integer.java:615)
    at Array.<init>(Array.java:16)
    at Array.main(Array.java:48)

I am totally not getting what's the issue. What I can guess is there is some issue while parsing the input stream. edit: when I press Enter after an input I get this :

shubham@shubham-Inspiron-3542:~$ java Array
Enter the size of the array : 5
Enter 5 integers
22
Exception in thread "main" java.lang.NullPointerException
    at Array.<init>(Array.java:16)
    at Array.main(Array.java:48)

edit 2: Splitting the input stream gets rid of NumberFormatException error but NullPointerException error is still there

`11 9 7 16 4` (note the spaces in between) is not a valid number. — domsson, Jun 01 '17 at 14:39
use readline().split(" ") and parse the string values into integer. — Lova Chittumuri, Jun 01 '17 at 14:45
That question does not fully answers mine one here as I have clearly instantiated the class Array as object a1 but still I am getting that error. My doubt now is if this is happening because I am instantiating the container class inside the main function. — Shubham, Jun 01 '17 at 16:47
okay, I have made a silly mistake and this is totally embarrassing. Apologies everyone, I never allocated memory to array[] . :( — Shubham, Jun 01 '17 at 17:01

score 0 · Accepted Answer · answered Jun 01 '17 at 14:39

0

This line you are reading: "11 9 7 16 4"

is not an integer, but a sequence of ints separated by a space.. you need to split those and then parse(convert them) everyone into an integer.

You should do something like:

String[] stringArray = br.readLine().split(" ");

then do the Integer.parseInt(...); on everyy element in that array.

answered Jun 01 '17 at 14:39

ΦXocę 웃 Пepeúpa ツ

47,427
17
69
97

after doing that I get: shubham@shubham-Inspiron-3542:~$ java Array Enter the size of the array : 5 Enter 5 integers 44 23 62 17 19 Exception in thread "main" java.lang.NullPointerException at Array.(Array.java:17) at Array.main(Array.java:49) – Shubham Jun 01 '17 at 14:50
ofcourse you will... array object is null.... – ΦXocę 웃 Пepeúpa ツ Jun 01 '17 at 14:52
I don't get it, how is array object null? – Shubham Jun 01 '17 at 14:56
I do have instantiated Array as a1 inside main() function – Shubham Jun 01 '17 at 16:51
Okay, this is embarrassing, I have realised my mistake. Sorry. – Shubham Jun 01 '17 at 17:00

NullPointerException and Array IO

1 Answers1