How is the NumberFormatException exception in Java generated?

The NumberFormatException in Java means that when converting a string to a numeric type and it is found that the string does not meet the format requirements of the numeric type, this exception will be generated. The following will discuss the causes, solutions and coping strategies of NumberFormatException exceptions from the following aspects.

1. Cause

In Java, when converting a string to a numeric type, the following conditions need to be met:

• String contains only numeric characters.
• The string contains only one positive and negative sign.
• The string contains only one decimal point.
• The string cannot contain spaces or other non-numeric characters.

If the string does not meet any of the above requirements, it will cause a NumberFormatException exception.

For example, execute the following code:

String str = "123.45a";
int num = Integer.parseInt(str);

Because the string contains the non-numeric character "a", a NumberFormatException exception will be thrown.

2. Solution

Java provides a variety of methods to avoid the occurrence of NumberFormatException exceptions.

• Use regular expressions to filter out non-numeric characters.

For example, you can use the following code to filter out non-numeric characters in a string:

String str = "123.45a";
str = str.replaceAll("[^\d.+-]", "");
int num = Integer.parseInt(str);

• Use a try-catch statement to catch exceptions.

For example, you can use the try-catch statement in the code to catch the NumberFormatException exception:

String str = "123.45a";
try {
    int num = Integer.parseInt(str);
} catch (NumberFormatException e) {
    e.printStackTrace();
}

• Use the numerical type parsing method to avoid exceptions.

Java provides a variety of numerical type parsing methods, such as parseInt, parseLong, parseDouble, etc. These methods will automatically filter out non-numeric characters in strings.

For example, you can use the following code to avoid the occurrence of NumberFormatException:

String str = "123.45a";
double num = Double.parseDouble(str);

3. Coping strategy

Reasonable strategies should be formulated for the occurrence of NumberFormatException. preventive solution. Here are some common strategies:

• Perform format checks on user-entered numbers. Add regular expression restrictions to the input box, or use a modified numeric keyboard to restrict users from entering illegal characters.
• Filter and convert strings. Use regular expressions or numeric parsing methods in your code to ensure that the string contains only numeric characters.
• Catch exceptions and prompt the user. Use the try-catch statement in the code to catch the NumberFormatException exception and issue a prompt to the user, prompting the user that the input string does not meet the number format requirements.

To sum up, the NumberFormatException exception occurs because the string does not meet the format requirements of the number type. In order to avoid exceptions, user input should be checked, input strings should be filtered and converted, and reasonable response strategies should be formulated.

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