Why Does My Java Scanner Throw an InputMismatchException After Correct Double Input?

Scanner double value - InputMismatchException

Question:
When using Scanner to read a double value in Java, why does it throw an InputMismatchException after the correct input is provided?

Cause:
The exception occurs when the input does not match the expected data type, usually due to a locale mismatch.

Solution:
To resolve the issue, specify the Locale when creating the Scanner object:

Scanner scanner = new Scanner(System.in).useLocale(Locale.US);

Explanation:
Each locale has its own set of decimal and thousand separators. For example, in the US locale, the decimal separator is a period ('.') while in many European locales, it's a comma (,).

When creating the Scanner object without specifying a locale, Java uses the default system locale. If the default locale uses a comma as the decimal separator and the input is entered with a period, the Scanner attempts to read the input as an integer, resulting in an InputMismatchException.

By specifying the US locale, we ensure that the Scanner expects a period as the decimal separator and correctly reads the input as a double value.

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