How to check if a String is numeric in Java

Question

How would you check if a String was a number before parsing it?

Answer 1

Regex Matching

Here is another example upgraded "CraigTP" regex matching with more validations.

public static boolean isNumeric(String str)
{
    return str.matches("^(?:(?:\\-{1})?\\d+(?:\\.{1}\\d+)?)$");
}

1. Only one negative sign - allowed and must be in beginning.
2. After negative sign there must be digit.
3. Only one decimal sign . allowed.
4. After decimal sign there must be digit.

Regex Test

1                  --                   **VALID**
1.                 --                   INVALID
1..                --                   INVALID
1.1                --                   **VALID**
1.1.1              --                   INVALID

-1                 --                   **VALID**
--1                --                   INVALID
-1.                --                   INVALID
-1.1               --                   **VALID**
-1.1.1             --                   INVALID