NumberFormatException in Java

Introduction to NumberFormatException in Java

It is thrown while converting a string of improper format to a numeric value like an integer or float. An example of improper format can be a string that has a boolean value. If this string is converted to a numeric value, then an exception is thrown. For instance, parsing a string that is null to an integer. It is an unchecked exception, also known as a run time exception. The try-catch block is used for handling this exception. When operating with the string, a parseInt() method is used for converting a string to an integer type. parseInt() method can be used in two ways as given below:

Both methods are used for converting a string to an integer. The only difference between these two syntaxes is the parameter radix. When radix=10, the first method is considered equivalent to that of the second method.

Constructors of NumberFormatException

What Causes NumberFormatException?

There are various problems related to formatting string which is improper. Here are a few important reasons for NumberFormatException:

• Null input string: Integer.parseInt("null");
• Input string which is empty: Float.parseFloat(“”);
• Leading or trailing white spaces in input string: Integer abc=new Integer(“ 123 “);
• Extra symbol in input string: Float.parseFloat(4,123);
• Input string with data which is non-numeric: Double.parseDouble(“FifityFive”);
• Alphanumeric input string: Integer.valueOf(“33.three”);
• Input string with exceeded range of datatype: Integer.parseInt(“1826589745243”);
• Type mismatch between the value of input string and its method: Integer.parseInt("12.33");

Example of NumberFormatException

Program to illustrate NumberFormatException in java. In this example, we will try to understand how and why NumberFormartException occurs.

Output:

Explanation: As per code, as soon as the user enters a number other than Integer like double or float then the NumberFormatException occurs.

Flow of the given code:

• Input is taken from user
• The input is parsed using parseInt
• If there is an error while parsing
• NumberFormatException is thrown
• Else Output is printed

How to Handle NumberFormatException?

The NumberFormatException in java can be handled in two ways:

1. Using the block try-catch : This involves surrounding the code that might cause the exception with a try block and handling the exception in a catch block. For example:

Output:

2. Using throws keyword : This involves declaring that a method might throw a specific exception and leaving it to the calling method to handle it. For example, a method that parses a string to an integer might declare that it throws a NumberFormatException if the string is not a valid integer. The calling method would then have to handle this exception using a try-catch block or declare that it throws the exception using the throws keyword.

For example:

Output: