How exactly do try and catch work?

Question

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"

try{
    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){
          if(!Character.isLetter(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
        if(isHit){
                System.out.printf("Hit!\n");
                mHits += letter;
        }
        else if(!isHit){
                System.out.printf("Miss!\n");
                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;" ?

Answer 1 · 2015-02-06T12:51:16Z

February 6, 2015 12:51pm

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.

Answer 2 · 2015-02-06T12:53:28Z

February 6, 2015 12:53pm

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 {}

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ShaoHsuan Duan

ShaoHsuan Duan

How exactly do try and catch work?

2 Answers

miguelcastro2

miguelcastro2

miguelcastro2

miguelcastro2

Craig Dennis

Craig Dennis