Counting the number of columns in a 2D array,

[KalEl]

I am trying to count the number of columns in a 2d array. I get an error with the method I wrote. Any help would be appreciated. This is what my instructor wrote on the board, and I can swear I copied it letter for letter. So what am I doing wrong?

    public static int sumLengths(int[] array)
    {
    	int count = 0; // keep count of number of columns per row
    	
    	for (int i = 0; i < array.length; i++)
    	{
    		count += array[i].getLength();
                      // array[i].length; does not work either
    	}
    	
    	return count;
    	
    }

This is what the compiler says:

C:\arrayStuff.java:62: int cannot be dereferenced
            count += array[i].getLength();
                             ^
C:\arrayStuff.java:62: inconvertible types
found   : <nulltype>
required: int
            count += array[i].getLength();
                                       ^
2 errors

I would appreciate any help :(

[DarrylBurke]

You mention a 2-dimensional array but the method you show accepts a parameter that is a simple (1-dimensional) array.

array[i] in your code is an int, not int[]

db

[CJSLMAN]

Like Daryl mentioned, you are working with a one dimension array. The array[i].getLength is not the proper use of the getLength method. sTry:
Array: getLength(Object array) : Array*«*java.lang.reflect*«*Java by API
CJSL

[Eranga]

array[i];

gives the i th element of the array.

array.length;

gives the length of the array

[KalEl]

Thanks a bunch for your help guys, but I'm still lost. How exactly then do I count the number of columns? Array.length will only return the number of rows, correct?

[hitmen]

array[0].length

[Norm]

Java arrays are wierd. For a 2 dim array, you can access the first "row" as a one dim array.
array.length returns the length of the array you are looking at.

How would you define rows and columns for an array?
array[rows][columns]
then array[0] would be the first row which is an array of columns length

Also the number of columns in each row can be different.
int anArray[][] = new int[3][];
anArray[0] = new int[2];
// leaves [1] empty
anArray[2] = new int[5];

Write a small test program with the above. Assign values to elements and use a loop to print out the results.

[Eranga]

In sense 2D array is an arrays of array, that means each array is an element of an array. See the following.

        int arr[][]; // Declaration
        arr = new int[2][3]; // Instantiation

if you are think about parenthesis elements should arranged as follows.

{ {1, 2, 3 }, {23, 56, 0 } }

have two arrays

{1, 2, 3} and {23, 56, 0 }

and each array has three elements.

Just an additional information.

[KalEl]

Thanks a bunch for all the help guys! I understand now what I did wrong. The parameter variable in the sumLengths method should say int[][] array opposed to int[] array. I got it working!

Thanks again!

[Eranga]

Yes, you have to pick the right parameter. With length and elements in correct type.