Need help writing Decryption Method in Java?

The following is the method I use for encrypting: public static String encryptMessage(String clearmessage, int numRows) { String message = ""; int numCols = clearmessage.length() / Rows; for (int ind = 0; ind < Rows; ind++) { for (int k = 0; k < numCols; k++) { int index = indices + k * Rows; encryptedmessage += clearmessage.charAt(index); } } return message; } However, I need help creating a method that will decrypt a method that has been encrypted in the above manner, columnar transposition. The method only has to be able to decrypt messages with padding, since without padding is harder to accomplish.