Question

If I want to show an exception in JAVA GUI that checks if the date format is correct or the date doesn't exist, and if no input is put in how do I do that. For example if the date format should be 01-11-2020, and user inputs 11/01/2020 inside the jTextField it will show an error exception message that format is wrong, and if the user inputs an invalid date, it will print that the date is invlaid, and if the user puts no value inside the text box, it willl print an exception message that there needs to be a value.

Please help.

Answer 1

A date is valid if it satisfies following constraints.

1. It should be in correct format. For example - dd/MM/yyyy.
2. It exist in reality. For example - 30/02/2015 is not exist so it is invalid.

For validating first constraint we are using Regular expressions and for second constraint setLenient() method of DateFormat class.

• By default setLenient() is true. Means, it won't check whether date exist in reality or not.
• To make it eligible for validating real dates we have to turn it off.

For example:

private static boolean isValidDate(String input) {
String formatString = "MM/dd/yyyy";

try {
SimpleDateFormat format = new SimpleDateFormat(formatString);
format.setLenient(false);
format.parse(input);
} catch (ParseException e) {
return false;
} catch (IllegalArgumentException e) {
return false;
}

return true;
}

public static void main(String[] args){
System.out.println(isValidDate("45/23/234")); // false
System.out.println(isValidDate("12/12/2111")); // true
}

The output will be false for first date in main function.

The output will be true for second date in main function.