How to resolve an unknownFormatConversionException?

It's typically difficult to debug code absent the source code. You can post your source code in various ways (sharing a workspace 'snapshot' link or using a markdown syntax to correctly format code). However, you've probably got an incorrect placeholder string (or maybe haven't saved since you made a mod). With the following code, I used %w as an example of an incorrect placeholder and then used the %s as a correct example.

import java.io.Console;

public class TreeStory {

    public static void main(String[] args) {
        Console console = System.console();
        /*  Some terms:
            noun - Person, place or thing
            verb - An action
            adjective - A description used to modify or describe a noun
            Enter your amazing code here!
        */
        String name  = console.readLine("Enter a name:");
        String adjective = console.readLine("Enter an adjective:");
        try {
          console.printf("%w is %s.", name, adjective); //throws an unknownFormatConversionException
        } catch (Exception e){
          console.printf(""+e.getClass());
        }
        console.printf("%s is %s.", name, adjective);
    }
}

Try/catch are just in the above so I can throw the error and then still demo the functioning code. With Java exceptions, you can typically just google them and look at the line number in the stacktrace to see where the problem is. Your stacktrace placed the error at line 15 in your code ("at TreeStory.main(TreeStory.java:15)").

The next video has some introductory content on debugging. I think they present compile time errors to start with. These are errors that prevent compilation. A runtime error is something where the program is able to compile and run, but crashes during execution. So it might look a little different to the errors he demos.