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Wednesday, March 27, 2019

Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = '-', = '#', = '.' - Solution

UnknownFormatConversionException in Java.  In this post, We will learn about UnknownFormatConversionException with some examples and common exception "Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = '-', = '#', = '.' - Solution".

 Unchecked exception thrown 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.

 NullPointerException in String contains method.

 UnknownFormatConversionException is child class of IllegalFormatException class.
UnknownFormatConversionException
UnknownFormatConversionException Constructor Syntax: 
public UnknownFormatConversionException(String s)


Constructs an instance of this class with the unknown conversion. s indicates the unknown conversion type or value.

UnknownFormatConversionException Methods: This has 2 methods as below.

 1) public String getConversion(): Returns the unknown conversion.
2) public String getMessage(): the detail message string of this Throwable instance (which may be null). This method is overridden method from Throwable class.
Example program on UnknownFormatConversionException: When we will get exception UnknownFormatConversionException:

 The following code throws this exception, and I'm not sure why. There is clearly a problem with outputting String.format to the formatedStr variable, but I don't know what's wrong with it.

 
package examples.java.w3schools.exceptions;

public class UnknownFormatConversionException {

 public static void main(String[] args) {
  String name = "Jhon";
  int age = 20;

  String formatedStr = String.format("Name : %s, Age : %i", name, age);
  System.out.println("formatedStr : " + formatedStr);
 }
}

Output:

Below is the exception full stack trace.

 
Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = 'i'
 at java.base/java.util.Formatter$FormatSpecifier.conversion(Formatter.java:2839)
 at java.base/java.util.Formatter$FormatSpecifier.(Formatter.java:2865)
 at java.base/java.util.Formatter.parse(Formatter.java:2713)
 at java.base/java.util.Formatter.format(Formatter.java:2655)
 at java.base/java.util.Formatter.format(Formatter.java:2609)
 at java.base/java.lang.String.format(String.java:2897)
 at w3schools/examples.java.w3schools.exceptions.UnknownFormatConversionException.main(UnknownFormatConversionException.java:9)


We will understand where the problem is. Just observe the reason for the exception that is "Conversion = 'i'". It is indicating that some problem with conversion type i.
In above code, used "%i" for integer which is causing for the error. 
Solution: To resolve the issue, we should reformat the code as below. For integer, must use 'd' instead of 'i'. This will resolve the problem.

String formatedStr = String.format("Name : %s, Age : %d", name, age);
Output: The above code will produce this output.

formatedStr : Name : Jhon, Age : 20
Another example program on UnknownFormatConversionException: In the below code snippet, we are trying to say the welcome to the Billy and used "%#" for type String content. We will run and see the output.
   String welcomeNote = String.format("Hello, Mr %# : Welcome to JavaW3schools blog :  ", "Billy");
   System.out.println("Welcome Note : " + welcomeNote);

Output: See the below output and seeing the conversion '#' is causing the problem which is invalid conversion type. To resolve, should use corresponding type that is "%s" in this case.
Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = '#'
 at java.base/java.util.Formatter$FormatSpecifier.conversion(Formatter.java:2839)
 at java.base/java.util.Formatter$FormatSpecifier.(Formatter.java:2865)
 at java.base/java.util.Formatter.parse(Formatter.java:2713)
 at java.base/java.util.Formatter.format(Formatter.java:2655)
 at java.base/java.util.Formatter.format(Formatter.java:2609)
 at java.base/java.lang.String.format(String.java:2897)
 at w3schools/examples.java.w3schools.exceptions.UnknownFormatConversionException.main(UnknownFormatConversionException.java:13)
UnknownFormatConversionException getConversion method example:
UnknownFormatConversionException-getMessage
This method returns the what conversion value causes for the problem. Refer the below example program.

 
public class UnknownFormatConversionExceptionMethods {

 public static void main(String[] args) {

  try {
   String welcomeNote = String.format("Hello, Mr %# : Welcome to JavaW3schools blog :  ", "Billy");
   System.out.println("Welcome Note : " + welcomeNote);
  } catch (java.util.UnknownFormatConversionException ex) {
   System.out.println("getConversion method value: " + ex.getConversion());
  }
 }
}


getConversion method Output: 
getConversion method value: #

UnknownFormatConversionException getMessage method example: getMessage method will provide the complete detailed reason for the error. Always better to go with this method rather than getting the conversion by invoking getConversion() method.

 
package examples.java.w3schools.exceptions;

public class UnknownFormatConversionExceptionMethods {

 public static void main(String[] args) {

  try {
   String welcomeNote = String.format("Hello, Mr %# : Welcome to JavaW3schools blog :  ", "Billy");
   System.out.println("Welcome Note : " + welcomeNote);
  } catch (java.util.UnknownFormatConversionException ex) {
   System.out.println("getMessage method value: " + ex.getMessage());
  }
 }
}


getMessage method Output: 
getMessage method value: Conversion = '#'

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