Question

I admittedly am not a Regular Expression expert, but would like to validate an input string and writing if/else statements for various validations just isn’t the way to do this. I’m using Java.

The input will be in the form a colon (:) separated tuple of three values. The first value will be an integer (potentially a long in terms of size/length), with the other two values being either numberic or a string.

For example, the following values would be valid:

• 1:x:456
• 2:2:3
• 3:abc:123

..and these would not:

• x:1:2
• 1::2
• 1:3::x
• 1:2
• fyz::2:1
• 1:3::3

Is there a relatively easy way to validate this input using a regular expression?

Answer 1

Matching Numbers:(letters OR numbers):(letters OR numbers)

If you want it such that it has to be numbers or letters only for 2nd and 3rd part, you can use this pattern:

String pattern = "^\\d+(:([A-Za-z]+|\\d+)){2}$";

Basically it will look for a sequence of numbers (\\d+), followed by a twice-repeated sequence of characters:

• starting with a a :, followed by
  • a sequence of letters (English), that is [A-Za-z], OR
  • a sequence of numbers

The ^ and $ characters are anchors, meaning “beginning-of-string” and “end-of-string”

Example:

public class RegexTest {
    public static void Main(String[] args) {
        String pattern = "^\\d+(:([A-Za-z]+|\\d+)){2}$";
        String example = "333:abc:123456";
        if (example.matches(pattern)) {
           System.out.println("Matches");
        }   
    }
}

Matching Numbers:(both letters and numbers:(both letters and numbers)

For this, you can use this pattern:

String pattern = "^\\d+(:[A-Za-z0-9]+){2}$";

Which will match:

• A series of digits, followed by
• A colon, followed by any combination of letters or numbers
  • repeat this sequence twice

---

   public class RegexTest {
        public static void Main(String[] args) {
            String pattern = "^\\d+(:[A-Za-z0-9]+){2}$";
            String example = "333:a3b4c:12adf3456";
            if (example.matches(pattern)) {
               System.out.println("Matches");
            }   
        }
    }

This example will match.