Java For-each loop data type mismatch

Question

I was converting a bunch of ordinary for loops to for-each loops in my most recent project and ran into a paradoxical problem.

    imgMap = new int[rows][cols];

    for (int r=0; r<imgMap.length; r++) {
        rowArray = mapBR.readLine().split(",");
        for (int c=0; c<imgMap[r].length; c++) {
            imgMap[r][c] = Integer.parseInt(rowArray[c]);
        }
    }

    System.out.println(imgMap.length+", "+imgMap[0].length);

    // print array in rectangular form
    for (int[] r : imgMap) {
        for (int[] c : imgMap[r]) {
            System.out.print(" " + c[0]);
        }
        System.out.println("");
    }

imgMap is a two-dimensional int array (int[][]) to hold a 'map'
mapBR is a BufferedReader of the external file that the 'map' is taken from
The first nested for loop set reads the file, the second nested for-each set writes it to the console to make sure that it is read correctly.

I couldn't see a way to make the first for loop set work as for-each loops so that is a sub-problem I would be delighted if someone could help me with as well.

Anyway, back to the main problem. when I (try to) compile this the compiler regurgitates an error saying that the int[] c : imgMap[r] line has incompatible types, but, and here's the catch, when I change it to int c : imgMap[r], it coughs up the same error! As I can't see how it could be any other than one of those types I am flummoxed.

I hope I have provided enough information.

IAmThePiGuy

thanks everyone who answered so quickly, it still amazes me the warmth of this online community. BTW, if someone could come up with a way to make the nested for set into a nested for-each set similarly I would be grateful. — cortices
– cortices, Commented Dec 15, 2010 at 9:16

Jon Skeet · Accepted Answer · 2010-12-15 09:13:10Z

5

In the first loop, you need c to be an int so that you can access rowArray[c] - but this should work:

for (int[] row : imgMap) {
    String[] rowArray = mapBR.readLine().split(",");
    for (int c = 0; c < row.length; c++) {
        row[c] = Integer.parseInt(rowArray[c]);            
    }
}

In the second loop, you just need to iterate through r, not through imgMap[r]:

for (int[] row : imgMap) {
    for (int value : row) {
        System.out.print(" " + value);
    }
    System.out.println("");
}

Basically, you need to think carefully about the types involved - whether a variable represents an index into an array, or the array itself.

answered Dec 15, 2010 at 9:13

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

cortices Over a year ago

Wow... I warranted an answer by THE Jon Skeet! Thanks, that's EXACTLY what I wanted.

Vladimir Ivanov · Accepted Answer · 2010-12-15 09:10:44Z

4

you're trying to use r, which is an int [], as just int. It is wrong. fix it to

for (int c : r) {
  ...
}

answered Dec 15, 2010 at 9:10

Vladimir Ivanov

43.2k19 gold badges80 silver badges103 bronze badges

Comments

Jigar Joshi · Accepted Answer · 2010-12-15 09:10:08Z

3

int[] c : imgMap[r]

as index of array it takes int and you have supplied int[]

It should be

   for (int[] r : imgMap) {
        for (int c : r) {
            System.out.print(" " + c);
        }
        System.out.println("");
    }

answered Dec 15, 2010 at 9:10

Jigar Joshi

241k42 gold badges409 silver badges446 bronze badges

Comments

Andreas Dolk · Accepted Answer · 2010-12-15 09:10:09Z

3

This is how it works:

for (int[] row : imgMap) {
  for (int cell : row) {
    System.out.print(" " + cell);
  }
  System.out.println("");
}

The outer for loop provides all rows from the matrix, the inner for loops all cells from a row.

answered Dec 15, 2010 at 9:10

Andreas Dolk

115k20 gold badges185 silver badges275 bronze badges

Comments

khachik · Accepted Answer · 2010-12-15 09:11:37Z

3

for (int[] r : imgMap) {
    for (int c : r) {
        System.out.print(" " + c);
    }
    System.out.println("");
}

answered Dec 15, 2010 at 9:11

khachik

28.8k10 gold badges63 silver badges98 bronze badges

Comments

kukudas · Accepted Answer · 2010-12-15 09:14:46Z

3

If i understand this correct it has to be like this:

for (int[] r : imgMap) {
        for (int c : r) {
            ...
        }
        ...
    }

answered Dec 15, 2010 at 9:14

kukudas

4,9545 gold badges47 silver badges66 bronze badges

Comments

sjngm · Accepted Answer · 2010-12-15 09:11:22Z

2

You'd need to code

for (int c : r)

answered Dec 15, 2010 at 9:11

sjngm

13k16 gold badges90 silver badges118 bronze badges

Collectives™ on Stack Overflow

Java For-each loop data type mismatch

7 Answers 7

1 Comment

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

1 Comment

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related