do {
number = (String)JOptionPane.showInputDialog(null,"Quantity : ","TRIAL",JOptionPane.QUESTION_MESSAGE);
if(number.matches("\\d+")) {
qty = Integer.parseInt(number);
}
// JOptionPane.showMessageDialog(null,"Invalid input !\n\nMin = 1\nMax = 100","TRIAL",JOptionPane.ERROR_MESSAGE);
} while(qty < 1 || qty > 100);
JOptionPane.showMessageDialog(null,number);
if I put the error message inside or outside if, the error message still appear if user key-in right data
You want to show the message if the input doesn't match the regular expression. So this:
if(number.matches("\\d+")){
qty = Integer.parseInt(number);
}
// JOptionPane.showMessageDialog(null,"Invalid input !\n\nMin = 1\nMax = 100","TRIAL",JOptionPane.ERROR_MESSAGE);
needs to become this:
if(number.matches("\\d+")){
qty = Integer.parseInt(number);
} else {
JOptionPane.showMessageDialog(null,"Invalid input !\n\nMin = 1\nMax = 100","TRIAL",JOptionPane.ERROR_MESSAGE);
}
Now you're saying that if it matches OK then you read the new value of qty, but if it doesn't then you show the message.
You might think about an alternative, which is to avoid the regular expression, but just attempt the parseInt() call, and then catch the NumberFormatException that results if it can't be converted.
(You also need some logic to show an error if the number can be parsed, but gives a result outside the valid range of 1 to 100.)
You can move a condition check into the loop and change your loop to infinite:
while (true) {
number = (String)JOptionPane.showInputDialog(null,"Quantity : ","TRIAL",JOptionPane.QUESTION_MESSAGE);
if(number.matches("[1-9]\\d*")){
qty = Integer.parseInt(number);
if (qty >= 1 && qty <= 100) {
break;
}
}
JOptionPane.showMessageDialog(null, "Invalid input !\n\nMin = 1\nMax = 100", "TRIAL", JOptionPane.ERROR_MESSAGE);
}
JOptionPane.showMessageDialog(null,number);
In that case, you have an infinite loop, which will break only if the entered value contains only digits and it's value is within the range [1,100]
[1-9]\d*. it will accept only numbers with 1-9 at the beginingHow do I call error message if user input wrong numeric data
I would instead suggest offering them a control which makes selecting a number, easy. Specifically, a spinner with a spinner number model. Like this:
import javax.swing.*;
public class PickANumber {
public static void main(String[] args) {
Runnable r = new Runnable() {
@Override
public void run() {
SpinnerNumberModel spinnerModel =
new SpinnerNumberModel(0, 0, 100, 1);
JSpinner spinner = new JSpinner(spinnerModel);
while (spinnerModel.getNumber().intValue()<1) {
JOptionPane.showMessageDialog(
null,
spinner,
"Pick a number between 1 & 100!",
JOptionPane.QUESTION_MESSAGE);
}
System.out.println(
"Number: " + spinnerModel.getNumber().intValue());
}
};
SwingUtilities.invokeLater(r);
}
}
