String to Character Array

Question

I have a problem with my code below:

public class stringToChar {
public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int n = in.nextInt();
    char[] sCharArr;
    String[] odd = new String[n];
    String[] even = new String[n];
    for(int i = 0; i < n; i++) {
        sCharArr = in.next().toCharArray();
        for(int j = 0; j < sCharArr.length; j++) {
            if(j % 2 == 0)
                even[i] += sCharArr[j];
            else
                odd[i] += sCharArr[j];
        }
   }
   for(int i = 0; i < n; i++) {
       System.out.println(even[i] + "  " + odd[i]);
   }
 }
}

My issue is on the output it has a Null in the result. Here is a sample scenario:

2
John
Cena

Answer should be:

Jh  on
Cn  ea

But my code answer is:

NullJh  Nullon
NullCn  Nullea

GhostCat · Accepted Answer · 2016-09-04 11:28:12Z

1

Your problem is that the new arrays are initialized with all null Strings. Then your code is not assigning values to all array elements, but just to some of them!

Finally you print your array, and surprise, those values that were null and that have not been changed - are still null (and when you print a null string ... it prints "null" [ yes, null, not Null; you got a little mistake there in your output example ]

You see, you iterate from 0 to the length of your two arrays. And if the number is even, you put a value in the even[i]; and if the value is odd, it goes to odd[i]. Lets take even - in that case, odd[i] simply stays null!

One way to fix that:

List<String> even = new ArrayList<>();
List<String> odd = new ArrayList<>();

And now, instead of setting a certain index in even/odd; you simply do:

even.add(some new value);

and to add those single characters:

even.add(new String(sCharArr));

Doing so, even and odd will (in the end) contain exactly the values that you added to each list; but no "residual" nulls. For the record: the way how you split up strings, to then pull them back into a String array isn't exactly the most simple/straight forward way to solve the problem.

But I leave "further" simplifications" as exercise to the user.

edited Sep 4, 2016 at 11:28

answered Sep 4, 2016 at 10:36

GhostCat

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4 Comments

Cham Over a year ago

Thank you!! Very helpful and informative, this is the answer to my issue!

Cham Over a year ago

I tried to add your suggestion, but I cannot add a single character in the List<String> I suppose that it should be a String type to be added. But since I converted the String to charArray how will I be able to add the char on the List<String>?

Cham Over a year ago

GhostCat thank you for the update however it outputs in on a single line mixing John and Cena, and it is enclosed in "[ ]".

GhostCat Over a year ago

That is because you are probably printing the whole list at once. Tried iterating it; as you did your array?

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