In the standard CodeHS Java (or JavaScript) track, is typically a coding exercise titled "Manipulating 2D Arrays" . While versions vary slightly, the general prompt involves writing methods that perform specific transformations on a 2D list (matrix), such as:
public static void manipulateArray(int[][] arr) // Traverse the rows for(int r = 0; r < arr.length; r++) // Traverse the columns in the current row for(int c = 0; c < arr[r].length; c++) // EXAMPLE: Double every value arr[r][c] = arr[r][c] * 2; Use code with caution. Key Takeaways for 8.1.5 tells you the number of rows. arr[r].length tells you the number of columns in row r . Always use [row][col] order when accessing elements.
: fixArray(array, 1, array[1].length - 1, totalElements);
Searching for a specific value within a grid is a practical skill. For instance, you can write a function to find a target value and return its coordinates. Codehs 8.1.5 Manipulating 2d Arrays
// Set all values in Row 1 to zero for (int c = 0; c < grid[1].length; c++) grid[1][c] = 0; // Set all values in Column 2 to 99 for (int r = 0; r < grid.length; r++) grid[r][2] = 99; Use code with caution. Algorithm C: Swapping Elements
for (int row = 0; row < grid.length; row++) for (int col = 0; col < grid[row].length; col++) // Multiply every element by 2 grid[row][col] = grid[row][col] * 2; Use code with caution. Nested for-each Loops (Reading Data)
For example:
return (double) total / (scores.length * scores[0].length);
Java 2D arrays are traversed using row-major order by default. This means your code reads or writes data across the first row from left to right, then moves down to the second row, and so on. You achieve this using nested for loops. The controls the current row. The inner loop controls the current column within that row. 2. The .length Property
Dynamic grid sizing prevents your code from breaking when the array size changes. matrix.length returns the total number of . In the standard CodeHS Java (or JavaScript) track,
public static void main(String[] args) int[][] test = 9, 8, 7, 6, 5, 4, 3, 2, 1 ;
To work with every element in a 2D array, you must use a : an outer loop for the rows and an inner loop for the columns. By default, this processes the array in row-major order , where the inner loop runs to completion for each iteration of the outer loop.
If you swap elements in the same loop where you iterate, you may double-swap. For column swaps, simply loop through rows; don't loop twice. // Set all values in Row 1 to
If your manipulation method requires a return value (like a modified array or a count), ensure your return statement sits outside the loops. Putting a return statement inside the inner loop will stop the method during the very first iteration.
When the autograder runs, it checks for specific output patterns. Before submitting, print your array using a helper method to visualize the changes: