access array elements in java outside the loop

Question

I am developing a simple program to print seat numbers, where the row are numbered from 1-5 and columns from a-e. the code i am using is as follows

public class JavaApplication5 {
    public static void main(String[] args) {
        int j =1,k;
        int i;
        char c;
        String[] arr = new String[25];
        for( i = 0;i < arr.length;i++)
        {
            while(j <= 5)
            {
                for(k = 97;k < 102; k++)
                {
                    c = ((char)k);
                    arr[i] = j + "" + c;
                    System.out.println(arr[i]);
                }
                j++;
            }
        }
    }
}

this displays desired result. but when I print an element outside the for loop I get the result as null like below

public static void main(String[] args) {
    int j =1,k;
    int i;
    char c;
    String[] arr = new String[25];
    for( i = 0;i < arr.length;i++)
    {
        while(j <= 5)
        {
            for(k = 97;k < 102; k++)
            {
                c = ((char)k);
                arr[i] = j + "" + c;
            }
            j++;
        }
    }
    System.out.println(arr[6]);
}

how to solve this?

If you have a solution which displays the desired result what is your question? — Kalle Richter
– Kalle Richter, Commented Sep 19, 2015 at 13:13

Manos Nikolaidis · Accepted Answer · 2015-09-19 13:02:30Z

1

this will leave all elements as null

String[] arr = new String[25];

this will iterate until j == 5 so only until arr[5]

while(j <= 5) {
   j++;
}

Therefore arr[6] is still null

answered Sep 19, 2015 at 13:02

Manos Nikolaidis

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Comments

Yassine.b · Accepted Answer · 2015-09-19 13:16:58Z

1

Change

arr[j] = j + "" + c;

instead of

arr[i] = j + "" + c;

Now it works.

public static void main(String[] args) {
    int j = 1, k;
    int i;
    char c;
    String[] arr = new String[25];
    for (i = 0; i < arr.length; i++) {
        while (j <= 5) {
            for (k = 97; k < 102; k++) {
                c = ((char) k);
                arr[j] = j + "" + c;
            }
            j++;
        }
    }
    System.out.println(arr[1]);
    System.out.println(arr[2]);
    System.out.println(arr[3]);
    System.out.println(arr[4]);
    System.out.println(arr[5]);
    System.out.println(arr[6]); // null because your check j <= 5 in while loop
}

edited Sep 19, 2015 at 13:16

answered Sep 19, 2015 at 13:05

Yassine.b

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Comments

Commodore Yournero · Accepted Answer · 2015-09-19 13:02:32Z

0

You can access the array elements normally outside of the loop. In your example, arr[6] is just null. The fault is not in the way you access it. (Although i cant see the bug yet ;))

answered Sep 19, 2015 at 13:02

Commodore Yournero

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Comments

A.v · Accepted Answer · 2015-09-19 13:24:42Z

0

The problem in your code is that you simply write 5 time on index 1, then 5 time on index 2 and so on. So you never wrote on index 6. Your code should be changed to code below:

String[] arr = new String[25];
int i = 0;
int j = 1;
while (j <= 5) {
    for (k = 97; k < 102; k++) {
        c = ((char) k);
        arr[i++] = j + "" + c;
    }
    j++;
}
System.out.println(arr[6]);

Because your loops run 5*5 times, then your i index will never pass arr array length. But you better control it like this to prevent your code from being error prone:

if(i < arr.length) {
    arr[i++] = j + "" + c;
} else {
    break;
}

answered Sep 19, 2015 at 13:24

A.v

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