Printing string array also prints null

Question

When I am printing contents of a string array the output is printing 'null' as well. I am not sure what's wrong with this. Here is the output, what I expect is the output without 'null'

null(wa?>=0)nullnull*(wo?>=0)nullnull*(4*wa?+7*wo?>=50)nullnull*(d1=10)nullnull*((d2=1)+(k=2))nullnull

Thanks and appreciate your help. I would say my skill in Java in beginner level and I started two weeks back.

Here is the actual code:

        String[] arrStr = new String[50];
        int countStr = 0;

        for (int i = 0; i < para.length; i++) {
            if (para[i] == '(') {
                count = count + 1;
            }
            if (para[i] == ')') {
                count = count - 1;
            }
            if (count > 0) {
                arrStr[countStr] = arrStr[countStr] + para[i];
            } else {
                if (para[i] == ')') {
                    arrStr[countStr] = arrStr[countStr] + para[i];
                    countStr += 1;
                } else {
                    countStr += 1;
                    arrStr[countStr] = arrStr[countStr] + para[i];
                    // System.out.println(para[i]);
                }
            }
        }
        System.out.println(countStr);

        for (int i = 0; i < countStr; i++) {
            System.out.print(arrStr[i]);
        }

Before this part, I am reading the following string from a word document:

(wa?>=0)AND(wo?>=0)AND(4*wa?+7*wo?>=50)AND(d1=10)AND((d2=1)+(k=2))

I think the problem may be due to the line:

arrStr[countStr] = arrStr[countStr] + para[i];

Since arrStr[countStr] is null initially and I add an element to it, it saves it as null+para[i]. Do you think it is possible?

Like when I try: System.out.println(arrStr[0]); I get the output as

null(wa?>=0)

If you need help debugging your code, the actual code would help. — Joachim Isaksson
– Joachim Isaksson, Commented May 27, 2013 at 15:39
After every assignment opeartion done on the array, print out the value that you have assigned. It will give you a better picture of where the value is being set as null. If you can provide th entire code, it would be easier to point out where the problem is. — Adarsh
– Adarsh, Commented May 27, 2013 at 15:58

njzk2 · Accepted Answer · 2013-05-27 16:04:22Z

3

System.out.println(null + "Bla");

prints nullBla. A null represented as String is "null". The issue here is that initially all your String[] is made of null. You need to initialize them first. Typically,

Arrays.fill(arrStr, "");

Should do.

answered May 27, 2013 at 16:04

njzk2

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1 Comment

user1596115 Over a year ago

Thanks that's what I thought. Really appreciate all of you for taking your time to answer :)

Makoto · Accepted Answer · 2013-05-27 15:45:55Z

0

If any element in arrStr is null while printing, it will print that faithfully.

Without knowing specifics in your code, you can either ensure that no element in your array becomes null (ensure that the lengths match up and you're not skipping element in arrStr, or check for null before printing the element.

answered May 27, 2013 at 15:45

Makoto

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Comments

eternay · Accepted Answer · 2013-05-27 16:04:46Z

0

You don't initialize the values of the arrStr array, you just allocate size for it, so each element of the array is null. When you assign a value to an element of the array, you concatenate its value (which is null) with the value of para[i].

You should initialize your array before using it:

String[] arrStr = new String[50];
for (int i = 0; i < arrStr.length; i++) {
    arrStr[i] = "";
}

answered May 27, 2013 at 16:04

eternay

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1 Comment

scottb Over a year ago

While this is an acceptable solution for this case, I hesitate to recommend this generally. In my opinion, it is better to design code that handles the possibility of nulls than to design code that expects that there will be no nulls and hopes for the best. The former should always end up being a more robust solution.

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