• Develop code used to traverse the elements in a 2D array and determine the result of these traversals

Assignment

The basic idea behind traversing a 2D array is to have an outer loop that will go target each array, and then a second, inner loop that goes though each element in the current array.1

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int[][] array = { { 1, 2, 3 }, { 4, 5, 6 } };

for (int row = 0; row < array.length; row++) {
    for (int col = 0; col < array[0].length; col++) {
        System.out.print(array[row][col] + " ");
    }
}

This approach is referred to as row-major due to the convention of thinking each of each array as a row in a table. You can also traverse an array using a column-major approach. The only thing that changes is the order of the loops.

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int[][] array = { { 1, 2, 3 }, { 4, 5, 6 } };

for (int col = 0; col < array[0].length; col++) {
    for (int row = 0; row < array.length; row++) {
        System.out.print(array[row][col] + " ");
    }
}

You can also used enhanced for loops, but only with a row-major traversal.2 Note the types used in each loop. The outer one needs to look at the inner arrays, so the type is int[]. The inner one looks at the actual values, so it’s int.

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

Lastly, use variable names that will be helpful in picturing the array. i and j tend to be used as counters for nested loops, but variables like row, col, and cell might make your life easier.

  1. Because we are assuming our 2D arrays are all rectangular, we can get away with using array[0].length on line 4. If each array was a different size, the safer approach would be to use array[row].length. ↩

  2. If you can do column-major with enhanced for loops, it’s likely more work than just using a regular loop. ↩