How to validate a string if it is a correct format in Java

Question

I am currently writing a validation method in Java to check if a string is in one of a few different format to be changed into a date.

The formats that I want it to accept are the following: MM/DD/YY , M/DD/YY, MM/D/YY, and M/D/YY.

I was testing the first format and every time it was telling me it was not valid even when I entered in a valid date.

Here is what my current code looks like:

public class IsDateFormatValid
{
   public boolean isValid(String date)
   {
      boolean result = true;
      if(date.length()>8||date.length()<6)
      {
         result= false;
      }
      if(date.length()==8)
      {
         if((Character.toString(date.charAt(2))!= "/")||(Character.toString(date.charAt(5))!="/"))
         {
            result=false;
         }   
      }
      if(date.length()==7)
      {
         if((Character.toString(date.charAt(2))!="/"&&Character.toString(date.charAt(1))!="/") ||(Character.toString(date.charAt(3))!="/"&&Character.toString(date.charAt(4))!= "/"))
         {
            result=false;
         }   
      }

      return result;   
   }
}   

I still need to put in the conditions for the last format case. I did a debug method and saw that the part that always returning false was the line that said: if((Character.toString(date.charAt(2))!= "/")||(Character.toString(date.charAt(5))!="/"))

The main point of this question is trying to check it against multiple formats not just a singular one how most other questions on here ask about.

Answer 1

You might want to iterate through possible formats, like this:

EXAMPLE:

private static String[] date_formats = {
        "yyyy-MM-dd",
        "yyyy/MM/dd",
        "dd/MM/yyyy",
        "dd-MM-yyyy",
        "yyyy MMM dd",
        "yyyy dd MMM",
        "dd MMM yyyy",
        "dd MMM yyyy"
};

/**
 * A brute-force workaround for Java's failure to accept "any arbitrary date format"
 */
public static Date tryDifferentFormats (String sDate) {
    Date myDate = null;
    for (String formatString : date_formats) {
        try {
            SimpleDateFormat format = new SimpleDateFormat(formatString);
            format.setLenient(false);
            myDate = format.parse(sDate);
            break;
        }
        catch (ParseException e) {
            // System.out.println("  fmt: " + formatString + ": FAIL");
        }
    }
    return myDate;
}