Way to find a correct date.

[Steven Villarreal]

I have been trying to figure out what is wrong with this code for quite some time. The point is to input a Date string lets say "5/10/2020". The code lets everything through the method that is 1/1, 1/12, 10/1, 10/11. But for instance, typing in a 0 before a day or month like 09, 012, 02 should throw a run time exception error. I got most of it to work except for one date which is "1/10" or having a one digit month and the day as 10, 20, or 30.

My code is here,

public GeoCountDownTimer(String geoDate) {
        if(geoDate.substring(0, 1).matches("[0]") || geoDate.substring(2, 3).matches("[0]") ||
            geoDate.substring(3, 4).matches("[0]")){
            throw new IllegalArgumentException();
        }

should I take,

geoDate.substring(3, 4).matches("[0]")

and replace that with

|| (geoDate.substring(3, 4).matches("[0]") && geoDate.substring(0,1).matches("[1-9]"))

I have tried that and it will not seem to work.

[Junilu Lacar]

You're over complicating this with matches(). I would just use String.startsWith() -- simple and straightforward.

[Steven Villarreal]

I visited the Java API and understood the startsWith method which is exactly what I needed. I just made two ifs, one with that method

if(geoDate.startsWith("0")){
            throw new RuntimeException();
}

and the other with the startsWith method and with

geoDate.substring(3,4).equals("0")

which looked like

if(geoDate.startsWith("0") && geoDate.substring(3,4).equals("0")) {
            throw new RuntimeException();
}

Thanks!

[Junilu Lacar]

You could have also used String.split() to make your code more readable.

String[] dateParts = someDate.split("/");

// some basic format checks
// like : should have 3 parts

if (valid(dateParts)) {
   //
} else {
   // ... throw exception
}

// indices into date parts array, assuming d/m/yyyy format
private static final int DAY = 0;
private static final int MONTH = 1;
private static final int YEAR = 2;

private boolean valid(String[] dateParts) {
   return startsWithDateDigit(dateParts[DAY]) && startsWithDateDigit(dateParts[MONTH]) && ... // whatever else
}

private boolean startsWithDateDigit(String value) {
   ...
}

Sure, it's a few lines longer that what you wrote but nobody has to spend a lot of time deciphering an expression like geoDate.substring(3, 4) (yuck) .

[Winston Gutkowski]

Steven Villarreal wrote:The point is to input a Date string lets say "5/10/2020". The code lets everything through the method that is 1/1, 1/12, 10/1, 10/11. But for instance, typing in a 0 before a day or month like 09, 012, 02 should throw a run time exception error.

Why? Seems perfectly reasonable to me (well, maybe not "012"), and the way many dates are actually written.

However, my advice would be to forget "rolling your own", and use the parser provided by SimpleDateFormat - ie, parse(String).

You should read up on it carefully first because there's quite a lot to know; but it's a far more generic solution and you don't have to write a single line of code.

The class even allows you to set its "strictness" (see setLenient(boolean)).

Winston