Java data format is not working in all scenarios

What is the mistake I did in my below code? If we do not pass date format like yyyy-MM-dd, it should throw parse error and it should return false but below one scenario not working

• 2020-08-19-->This is working fine and returning true
• 2020-19-08-->This is working fine and returning false
• 20-08-19-->This should return false. It is not working and returning true

I am not understanding why third scenario getting failed.

Clarification: I am asking: if we pass input: 20-19-08, it should return false, right? But its returning true. My problem is, if I pass 20 instead of 2020, it should return false.

Code

	public static boolean validateDateFormat(String strDate) {
		SimpleDateFormat sdfrmt = new SimpleDateFormat("yyyy-MM-dd");
		sdfrmt.setLenient(false);
		try {
			sdfrmt.parse(strDate);
		}
		catch (ParseException e) {
			return false;
		}
		return true;
	}

20-19-08 does not follow the format because the year is not specified as a four digit number (though the formatter you are using will recognize both 20 and 2020 as valid years, just not the same year) and your month value according to the format string will come up as 19, which is not valid.

You are not throwing the exception in catch block. hence it does not throw anything simply retyurn false. To get the actual exception throw it or printStackTrace() it.

This approach should be working for both conditions :

import java.util.*;
import java.text.SimpleDateFormat;


public class Main{
	public static void main(String[] args) {

        String ss = "20-19-08";
        if(validateDateFormat(ss)){
            System.out.println("SUCCESS");
        }else {
            System.out.println("ERROR");
        }
        
	}
	
	public static boolean validateDateFormat(String strDate) {
        SimpleDateFormat sdfrmt = new SimpleDateFormat("yyyy-dd-MM");
        sdfrmt.setLenient(false);
        try {
            Date date = sdfrmt.parse(strDate);
            System.out.println("Formatted Date :: "+date);
            return true;
        }
        catch (Exception e) {
            return false;
        }
    }
}

Test results :

Input : 20-19-08
Output : 

Formatted Date :: Mon Aug 19 00:00:00 UTC 20
SUCCESS

Input : 2020-19-08
Output :

Formatted Date :: Wed Aug 19 00:00:00 UTC 2020
SUCCESS

java.time

I don’t think SimpleDateFormat is able to give you the validation you are asking for. Which is just the same since that class is notoriously troublesome and long outdated. You shouldn’t use it anyway. I recommend that you use java.time, the modern Java date and time API, for all of your date work. And it validates your date string nicely. Use DateTimeFormatter.ISO_LOCAL_DATE.

public static boolean validateDateFormat(String strDate) {
try {
DateTimeFormatter.ISO_LOCAL_DATE.parse(strDate);
}
catch (DateTimeParseException e) {
return false;
}
return true;
}

Try it out:

	String candidate = "20-08-19";
boolean valid = validateDateFormat(candidate);
System.out.format("Is %s valid? %s%n", candidate, valid);

Output is:

> Is 20-08-19 valid? false

We can try some other strings too:

> Is 2020-13-19 valid? false
> Is 2020-08-19 and some more text that should not be here valid? false

And a valid one:

> Is 2020-08-19 valid? true

Why didn’t your code work?

> i am not understanding why second scenario getting failed can some one
> help me please

This is the way SimpleDateFormat parses numbers. From the documentation:

> - Year: If the formatter's Calendar is the Gregorian calendar, the following rules are applied.
> - …
> - For parsing, if the number of pattern letters is more than 2, the year is interpreted literally, regardless of the number of digits.
> So using the pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12
> A.D.
> - …

I think the example matches your situation pretty nicely. Even though you use yyyy in the format pattern string, SimpleDateFormat is happy to parse 20 as year 20 AD. This would explain why no exception is thrown, which in turn causes your method to return true.

Link

Oracle tutorial: Date Time explaining how to use java.time.