Handling Exception: Is the first line is System.out.println necessary?

To simply answer your question, no, since both of your print statements are doing similar operations. It's a bit redundant to add that first println statement. The only difference between your print statements is that your printf statement is invoking the 'getMessage()' method.

By looking at the Throwable class documention, it shows that the 'getMessage()' method returns the detail message string of this throwable.

"Returns: the detail message string of this Throwable instance (which may be null)." - from the documentation.

You can invoke the getMessage method from a println or printf statement like so:

//Exception variable name of 'e'
System.out.println("Something went wrong " + e.getMessage());  //println statement
System.out.printf("Something went wrong %s", e.getMessage());  //printf statement

Here's a basic example of the getMessage() method just so you have a better idea of how it works:

import java.io.*;
public class ExceptionPractice {
    public static void main(String[] args) {
        try { 
            methodThatThrowsAnIOException(); 
        } catch (IOException ioe) {
            System.out.println("Yikes!: " + ioe.getMessage());
        } 
    }        

    private static void methodThatThrowsAnIOException() throws IOException { 
        throw new IOException("An IOException occurred");
    } 
} 

The output for the above example is:

Yikes!: An IOException occurred

Regarding the code challenge that's testing you on exception handling, in the first code challenge 'throwing exceptions'. It say's (Okay, so let's throw an IllegalArgumentException from the drive method if the requested number of laps cannot be completed on the current battery level. Make the exception message "Not enough battery remains").

So, if mBarsCount is less than the number of laps, an IllegalArgumentException is thrown from your drive method, and your getMessage will log "Not enough battery remains". Said IllegalArgumentException is caught and handled in your try-catch block that you added your print statement to in the second code challenge "Handling exceptions".

In your catch block, if you add something like System.out.println("Uh-oh: " + e.getMessage()); your output would be: "Uh-oh: Not enough battery remains".

Let me know if you have any other questions, happy coding. :)

If you want to read more about the getMessage method/Throwable class you can find it here: https://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html#getMessage()

And you can also read more about the Exception class here: https://docs.oracle.com/javase/7/docs/api/java/lang/Exception.html