Java, Java Issues & Solutions

[Solved]java.util.UnknownFormatConversionException: Conversion = ‘I’

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java.util.UnknownFormatConversionException is runtime unchecked exception which throw when an unknown conversion is given. Unless otherwise specified, passing a null argument to any method or constructor in this class will cause a NullPointerException to be thrown.

  • UnknownFormatConversionException is sub class of IllegalFormatException.

Constructors

  • UnknownFormatConversionException(String s) : Constructs an instance of this class with the unknown conversion.

Example of UnknownFormatConversionException

In this below example by mistake use “Index” with specifiers sign (%) where considering ‘I’ as specifiers which is not match with predefined specifiers that’s what throwing this exception.

try
{
Scanner sc = new Scanner(new File("C:\Users\saurabh.gupta1\Desktop\testdata.txt"));
int i=0;
while (sc.hasNextLine()) {
//System.out.println(sc.nextLine());
Scanner lineScanner = new Scanner(sc.nextLine());
lineScanner.useDelimiter("|");
if(i==0)
{
System.out.format("%-10Index%-10s%-10s%-10s%-10sn", sc.next(),sc.next(),sc.next(),sc.next(),sc.next());
}
else
{
i++;
System.out.format("%-10d%-10s%-10s%-10s%-10sn", i,sc.next(),sc.next(),sc.next(),sc.next(),sc.next());
}
}
}
catch(Exception ex)
{
ex.printStackTrace();
}

Output

java.util.UnknownFormatConversionException: Conversion = 'I'
at java.util.Formatter$FormatSpecifier.conversion(Unknown Source)
at java.util.Formatter$FormatSpecifier.<init>(Unknown Source)
at java.util.Formatter.parse(Unknown Source)
at java.util.Formatter.format(Unknown Source)
at java.io.PrintStream.format(Unknown Source)
at com.userinput.JavaScannerParsingExample.main(JavaScannerParsingExample.java:45)

Solution

Always follow formatting specifiers rules as given in Java formatter.

https://docs.oracle.com/javase/10/docs/api/java/util/Formatter.html

References

https://docs.oracle.com/javase/8/docs/api/java/util/UnknownFormatConversionException.html

Know More

To know more about Java Exception Hierarchy, in-built exception , checked exception, unchecked exceptions and solutions. You can learn about Exception Handling in override methods and lots more. You can follow below links:  s