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Java Java Objects (Retired) Delivering the MVP Validation

ShaoHsuan Duan
ShaoHsuan Duan
6,044 Points

How exactly do try and catch work?

Hello, I'm really confused about how try and catch actually work and am trying to clarify my mind in this question.

Here is the part of "try" and "catch"

    isHit = mGame.applyGuess(guess);
    isValidGuess = true;
catch (IllegalArgumentException iae){
           console.printf("%sPlease try again.\n", iae.getMessage());

And here is the part of "throw new exception" along with the "applyGuess" method

      private char validLetter(char letter){
              throw new IllegalArgumentException("A letter is required\n");
          if(mHits.indexOf(letter)>=0 || mMisses.indexOf(letter)>=0){
              throw new IllegalArgumentException("You have tried this letter brfore.\n");}

          letter = Character.toLowerCase(letter);
          return letter;

    public boolean applyGuess(char letter) //see if the letter hit
        letter = validLetter(letter);

        boolean isHit = mAnswer.indexOf(letter)>=0;   //if mAnswer contains the letter the player entered. if yes, you'll get the index of the letter, if no, you'll get -1
                mHits += letter;
        else if(!isHit){
                mMisses += letter;
        return isHit;

My question is, if the exceptions in "validLetter()" happen, does "letter = validLetter(letter);" break the "applyGuess()" method?

And does this result the inability of executing this line "isHit = mGame.applyGuess(guess);" and break the "try block" and so it won't continue execute the next line which is "isValidGuess = true;" ?

2 Answers

When the applyGuess() method runs it will immediately call the validLetter() method to check if the letter is a valid character. If not, validLetter() will throw an exception. The exception is triggered on the line when applyGuess() is called:

isHit = mGame.applyGuess(guess);

When the exception is thrown, the code will stop processing and immediately jump to the catch{} block. The line:

isValidGuess = true;

Will never run.

One last thing, the applyGuess() method must throw an IllegalArgumentException() if there is not try/catch block within the method:

public boolean applyGuess(char letter) throws IllegalArgumentException {}
Craig Dennis
Craig Dennis
Treehouse Teacher

This isn't required as that is a RuntimeException, but thanks for the good practice.