compiler error: Array required, but java.lang.String found

Question

So I've looked at "questions that may already have my answer" but, despite getting the same error message as those questions, I think I may have a different issue:

//find greatest product generated by 5 consecutive integers below

class project_euler8 {

    public static String numbers = 
    "73167176531330624919225119674426574742355349194934" +
    "96983520312774506326239578318016984801869478851843" +
    "85861560789112949495459501737958331952853208805511" +
    "12540698747158523863050715693290963295227443043557" +
    "66896648950445244523161731856403098711121722383113" +
    "62229893423380308135336276614282806444486645238749" +
    "30358907296290491560440772390713810515859307960866" +
    "70172427121883998797908792274921901699720888093776" +
    "65727333001053367881220235421809751254540594752243" +
    "52584907711670556013604839586446706324415722155397" +
    "53697817977846174064955149290862569321978468622482" +
    "83972241375657056057490261407972968652414535100474" +
    "82166370484403199890008895243450658541227588666881" +
    "16427171479924442928230863465674813919123162824586" +
    "17866458359124566529476545682848912883142607690042" +
    "24219022671055626321111109370544217506941658960408" +
    "07198403850962455444362981230987879927244284909188" +
    "84580156166097919133875499200524063689912560717606" +
    "05886116467109405077541002256983155200055935729725" +
    "71636269561882670428252483600823257530420752963450"; 

    public static int calculateProduct(int[] myArray) {
        int product = 1;
        for (int i = 0; i < myArray.length; i++) {
            product *= myArray[i];
        }
        return product;
    }

    public static void main(String[] args) {
        //declare biggest_product, temporary array
        int biggest_product = 0;
        int[] temp = new int[5];
        //loop through each sequence of 5 integers
            for (int i = 0; i < numbers.length() - 5; i++) {
                int remainder = i % 5;
                **temp[remainder] = Integer.parseInt(numbers[i]);**
                int candidate_product = calculateProduct(temp);
                if (candidate_product > biggest_product) {
                    biggest_product = candidate_product;
                }
            }
        System.out.println("Biggest product is " + biggest_product);
    }

The line the compiler doesn't like is bolded above. If I declare my array (temp) within the for loop, will this fix the issue? I'm a bit confused why I can't assign integer values element-wise based on array index...

I know arrays in Java are immutable but, if this were the case, how could I assign values at any point after array declaration?

Oh, and arrays aren't immutable. They're very much mutable. — Makoto
– Makoto, Commented Jun 1, 2014 at 19:27
@OliCharlesworth Thanks for the help. I've modified that part to be: temp[remainder] = Integer.parseInt(numbers.charAt(i));...would you expect that to work? Compiler "can't find symbol" for method parseInt(char)...Thanks again! — anon_swe
– anon_swe, Commented Jun 1, 2014 at 19:27

Makoto · Accepted Answer · 2014-06-01 19:26:53Z

2

numbers isn't declared as an array; it is instead a String.

If you wanted to iterate over each character in the String, then that can be accomplished by numbers.charAt(i).

However, since what you're getting back is a char and not a String, you have to convert it appropriately (that is, subtract '0' from your numerical character to normalize it).

Since a char really is an int (with a shorter range), there's no convenience method in Integer to convert from a char to an int, so one has to subtract the char '0' to get a number back.

That solution would look something like this:

temp[remainder] = numbers.charAt(i) - '0';

This means that you have more work to do in changing the signature of your method that accepts an int[], but I leave that as an exercise for the reader.

answered Jun 1, 2014 at 19:26

Makoto

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Piotr Praszmo · Accepted Answer · 2014-06-01 19:32:05Z

0

It looks like you want to extract five digits from i to i+5. You can achieve this with substring method.

Instead of:

temp[remainder] = Integer.parseInt(numbers[i]);

do:

temp[remainder] = Integer.parseInt(numbers.substring(i,i+5));

answered Jun 1, 2014 at 19:32

Piotr Praszmo

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Makoto Over a year ago

I thought about that too, but that's not 100% true to the original operation. Getting the value at a single position is different than getting the values for a given range. Perhaps this would be a more ideal solution if the code were rewritten to make use of the fact that one is getting five numbers at a time instead of one.

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