What are the common causes of NumberFormatException in Java?

NumberFormatException in Java is a common exception that usually occurs when a string is converted to a numeric type. This article will explore the causes and solutions of NumberFormatException exceptions.

Cause of NumberFormatException exception:

1. The format is wrong when converting a string into a numerical type. For example, for the string "abc", the numeric type cannot be converted into a numeric value, so a NumberFormatException is thrown.
2. When the string is converted to a numeric type, it exceeds the range of the numeric type. For example, for the string "2147483648", it exceeds the upper limit of the integer type, so a NumberFormatException will be thrown.
3. The string contains illegal characters. For example, if the string contains spaces or other non-numeric characters, such as "10.5", these illegal characters will also cause a NumberFormatException exception.
4. The string contains leading or trailing spaces. In this case, the string may not be correctly converted to a numeric type, causing a NumberFormatException exception to be thrown.
5. The string is empty or has a length of 0. In this case, the numeric type cannot obtain a value from an empty string or a string of length 0, thus triggering a NumberFormatException exception.

How to solve the NumberFormatException exception:

1. Check the string format. Before converting a string to a numeric type, make sure it is formatted correctly. Regular expressions can be used to verify that strings meet specific format requirements.
2. Check the data range. Before converting a string to a numeric type, make sure it does not exceed the range of the numeric type.
3. Check whether the string contains illegal characters. Use the java.lang.Character.isDigit() method to check whether all characters in a string are digits.
4. Remove leading or trailing spaces from the string. Use the String.trim() method to remove leading or trailing spaces from a string.
5. Check whether the string is empty or has a length of 0. You can check if a string is empty using the String.isEmpty() method.

Finally, since NumberFormatException is common when converting strings into numerical types, in order to avoid exceptions being thrown, conversion operations involving strings in the code should be handled with caution. When using methods such as Integer.parseInt() and Double.parseDouble(), be sure to take precautions to ensure that the code can correctly handle correctly formatted and legal strings.

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