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Java Java Objects (Retired) Delivering the MVP Validation

Posted by Ivan Yudhi
Ivan Yudhi
2,031 Points

When to use IllegalArgumentException?

For this part of code exercise:

private char validateGuess(char letter) {
        //throw an exception error if not a letter
        if (!Character.isLetter(letter)) {
            throw new IllegalArgumentException("A letter is required");
        }
        //convert the letter to lowercase
        letter = Character.toLowerCase(letter);
        //check if the letter has already been guessed
        if(mMisses.indexOf(letter) >= 0 || mHits.indexOf(letter) >= 0) {
            throw new IllegalArgumentException(letter + " has already been guessed" );
        }
        return letter;
    }

Why do we need to throw IllegalArgumentException? Can't we just do println("message") to display the message, or does it serve other purpose?

Dan Johnson
Dan Johnson
40,533 Points
Dan Johnson
Dan Johnson
40,533 Points

Added code formatting.

1 Answer

Dan Johnson
Dan Johnson
40,533 Points
Dan Johnson
Dan Johnson
40,533 Points

Throwing an exception allows you to break out of the current block of code and process the error in a catch block. In the case of someone passing in something that wasn't a letter, it wouldn't make sense to further process it in the method.

try {
    validateGuess(5);
}
catch(IllegalArgumentException e) {
    //Would jump from the throw to here.
    System.out.println(e.getMessage());
    //Do more error handling if needed.
}
//Continue on from here