Monat: Dezember 2023

In my previous article about Fuzzing in Java, I encountered an interesting NumberFormatException: „Character array is missing „e“ notation exponential mark“. That one sparked a lot of curiosity. Today, let’s take a closer look at what exactly this error message means.

What Does This NumberFormatException Mean?

Let’s start with a simplified version of a method, dollar2euro, which converts a USD input to EUR:

public String dollar2euro(Object input){
    BigDecimal inputParsed = new BigDecimal(input.toString());
    BigDecimal dollars = inputParsed.setScale(2, BigDecimal.ROUND_HALF_EVEN);

    BigDecimal multiply = dollars.multiply(BigDecimal.valueOf(0.92));
    BigDecimal euros = multiply.setScale(2, BigDecimal.ROUND_HALF_EVEN);
    return String.valueOf(euros);
}

Now, suppose we call this method using the string "뤇皽" as input.
This would produce the following error:

Input: 뤇皽
java.lang.NumberFormatException: Character 뤇 is neither a decimal digit number, decimal point, nor "e" notation exponential mark.

The message tells us that the character 뤇 is neither a decimal digit, a decimal point, nor an „e“ used in exponential notation. In mathematics and programming, exponential notation expresses numbers like 1e3 to represent 1000 compactly. Java expects input strings for BigDecimal to contain only valid number representations — digits, decimal points, or the character e for exponents.

Since „뤇“ is none of these, Java immediately throws a NumberFormatException.

How Can You Avoid This Error?

To prevent this error, we should ensure that the value passed to the BigDecimal constructor is a valid number.
Ideally, you would work directly with numeric types like double or int whenever possible.

In our method, this would only require a small change to the parameter type and the parsing logic.

If you still prefer to work with String inputs, make sure the string represents a valid number format.
An example of a valid input would be:

"1337.012342„

By sticking to properly formatted input, you can avoid NumberFormatException issues like the one described here.

One side note here: Proper validation of user input is a critical security measure recommended by OWASP to prevent injection vulnerabilities and ensure application robustness. Using and handling this exception may help you here depending on your use case.

Conclusion

I hope this article helped clarify what the error „Character array is missing ‚e‘ notation exponential mark“ means in Java. While today’s example was constructed for clarity, such issues often arise unexpectedly when dealing with user input or external data sources.

If you have encountered a similar error in a real-world scenario, feel free to share it in the comments. I would be happy to take a look!

If you’re interested in diving deeper into testing and automation, you might enjoy my tutorials on Selenium with Java and Selenium with Python.
Or, if you want something a little more adventurous, check out my Cucumber in Rust tutorial.

Happy testing and have a great day!