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


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

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