Switch Rows and Columns 2d Array

Question

I want to swap Columns and Rows in a 2D array.

My problem is that I want the Variable "oldField" to save the oldField. The Variable I think is Pointing on the same Object as newField and so it get´s changed even tho I dont want that.

Id like to know how I can save the Variable oldField independent

public int[][] swapMatrix(int[][] pField) { // swaps the rows and columns in
                                            // a Field
    int[][] oldField = pField.clone();
    int[][] newField = pField.clone();
    for (int i = 0; i < newField.length; i++) {
        for (int j = (newField.length - 1); j >= 0; j--) {
            newField[i][(newField.length - 1) - j] = oldField[j][i];
        }
    }
    return newField;

}

Possible duplicate of [How do you rotate a two dimensional array?](https://stackoverflow.com/questions/42519/how-do-you-rotate-a-two-dimensional-array) — xenteros, Jun 08 '17 at 11:01

score 1 · Answer 1 · answered Jun 08 '17 at 10:51

When you copy in 1-D array with primitive value like int then the new array and content copy to it and there is no reference.

 int row1[] = {0,1,2,3};
    int row2[] =  row1.clone();
    row2[0] = 10;
    System.out.println(row1[0] == row2[0]); // prints false

but for 2-D array the content is object and clone method only do shallow copy not create new content if object is there .For your requirement you need to do deep copy.

int table1[][]={{0,1,2,3},{11,12,13,14}};
    int table2[][] = table1.clone();
    table2[0][0] = 100;
    System.out.println(table1[0][0] == table2[0][0]); //prints true

score 1 · Answer 2 · answered Jun 08 '17 at 11:06

this code solves your problem:

public class SwapRowsAndColumns {

    public static void main(String[] args) {

        int[][] someMatrix = new int[2][3];

        someMatrix[0][0] = 1;
        someMatrix[0][1] = 2;
        someMatrix[0][2] = 3;

        someMatrix[1][0] = 4;
        someMatrix[1][1] = 5;
        someMatrix[1][2] = 6;

        printMatrix(someMatrix);
        int[][] invertedMatrix = swapMatrix(someMatrix);
        printMatrix(invertedMatrix);

    }

    private static int[][] swapMatrix(int[][] pField) {

        int originalTotalRows = pField.length;
        int originalTotalColumns = pField[0].length;

        int[][] newMatrix = new int[originalTotalColumns][originalTotalRows];

        for(int i=0; i< originalTotalRows; i++){
            for(int j=0; j < originalTotalColumns; j++){
                newMatrix[j][i] = pField[i][j];
            }
        }
        return newMatrix;
    }

    private static void printMatrix(int[][] matrix){
        int totalRows = matrix.length;
        int totalColumns = matrix[0].length;

        for(int i=0; i< totalRows; i++){
            for(int j=0; j< totalColumns; j++){
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println("");
        }
    }
}

ty, I copied the Matrix with 2x for(){...} now it works just fine — Johannes Zahn, Jun 08 '17 at 11:43

Switch Rows and Columns 2d Array

2 Answers2