You have to add the parseInt method in try-catch block. Also modify the condition to be number < 1 || number > 9. finally you have to initialize the number with invalid value, lets say -1
String error = "Write a number below, between 1-9;";
int number = -1;
do {
try {
String userentered = JOptionPane.showInputDialog(error);
number = Integer.parseInt(userentered);
if (number < 1 || number > 9) {
error = "Error";
}
} catch (HeadlessException | NumberFormatException e) {
error = "Error";
}
} while (number < 1 || number > 9);