How to print a message if the do while loop condition is not met

Question

How would I print a message saying "Error: you have to enter a number between 0 and 5", then allowing the user to input again

 int number;
 do 
  {
     String textinput = JOptionPane.showInputDialog("give me a number between 0 and 5");
     number = Integer.parseInt(textinput);
  } while (!(number >= 0 && number <= 5));

Answer 1

The simplest method which alters your original code the least is as follows:

int number;
do {
    String textinput = JOptionPane.showInputDialog("give me a number between 0 and 5");
    number = Integer.parseInt(textinput);
    if((number < 0) || (number > 5) {
        //show error message
        continue;  //continue isn't absolutely necessary here, but perhaps for readability
    }
} while (!(number >= 0 && number <= 5));

Although I find this a little clunky and redundant, you're essentially checking the same condition twice. I'd go with a method more like the following:

int number;
String textinput = JOptionPane.showInputDialog("give me a number between 0 and 5");
while(true) {
    number = Integer.parseInt(textinput);
    if((number >= 0 && number <= 5)) {
        //show error message and prompt for another input
        contine; //As with before, continue isn't necessary here, but could add readability
    } else /*input was good*/ { break; /*exit while loop*/ }
}