while loop evaluation confusion

Thanks for the reply Evan.

So can I say interpret the while statement as the following:

1. In order to run the game for the first time, we need to define a isValidGuess and needs to set it to true(thats why ! isValidGuess), so we can pass it through the while loop for the first time? (Not quite sure about this still)

2. If the word we guess is valid, we move onto try block and run the applyGuess method as well as setting the isValidGuess variable to true. Since isValidGuess is true, we start the while loop all over again, without activating the catch iae block.

3. If the word we guess is not valid, we skip the entire try block, and onto the catch iae block, since the isValidGuess is still true, we will start the while loop all over again with the exception of running the applyGuess method. (ps. I have tried adding isValidGuess = true; at the end of the catch block, and it works just fine)

} catch (IllegalArgumentException iae) {
    console.printf("%s.  Please try again.\n", iae.getMessage());
    isValidGuess = true;
}

Hope I am not wrong. thanks again. Ray

Hi Ray,

1) isValidGuess needs to be false for the while loop to run, because the while loop takes not isValidGuess as its condition to run or not. If isValidGuess were true by default instead of false, then not true == false; the while loop would not run.

2) If the letter we enter is valid, isValidGuess is set to true, making the loop false - because the while condition is looking for the opposite of whatever isValidGuess is to determine true or false. A false while loop in the promptForGuess method means that the play() function checks whether its while loop is valid and if so, runs displayProgress() and promptForGuess() again. This goes back to why your always true isValidGuess looped the displayProgress() indefinitely; because the while loop checks !isValidGuess, it was actually always false.

3) If our guess is invalid, we skip the try block (which includes the isValidGuess = true), which means isValidGuess is still false, and not false == true so the loop runs again. Bear in mind that 'not valid' in this case means that validateGuess() is checking whether you entered a number or a letter that's already been guessed. Adding isValidGuess = true to then end of your catch block works fine, because if you break the while loop of promptForGuess(), the while loop of the play() method will just run the displayProgress() and promptForGuess() functions again as long as its own while loop is resulting true.

Great answer Evan !!!!!!!!!!!

Evan, thanks a lot for the help, ok so i think I am nearly getting it. Correct me if I am wrong.

1. In short, for boolean variables to run in while loop, it has to be true? (P.S I tried setting isValidGuess to true at the begining, therefore i put while (isValidGuess), also changing the isValidGuess = true into isValidGuess = false in the try block, everything works just fine.)

2. In short, if the word is valid, we run mGameApplyGuess() method as well as setting the isValidGuess variable to be the opposite as what we put in the while loop, the reason for that is because we want the opposite of what is in the while loop, so we do not enter it again?

3. In short, if the word is invalid, we skip the try block, and onto the catch block, since isValidGuess is still false, the while loop is still saying "not false" which is true, so the while loop will run until it goes into the try block? (P.S Adding either isValidGuess = true or isValidGuess = false don't matter at all for the end result).

Thanks again for helping me out.

Ray

That's correct. While loops will only ever run their code if the condition is true.

while(true) {
  // will run this code
}

while(false) {
  // will not run this code
}

That means that "isValidGuess", which is false could never run the while loop all by its lonesome.

However, through the magic of negation (the ! operator) you flip it to "not false", which is true, and get it to run. :)

while(! somethingFalse) {
}

// really looks like this, because you're plugging in the **opposite** of the value actually held there

while(not false)

// which is...

while(true)

Java while and do-while documentation will come in handy.

Take a look at the do-while statement, which you'll learn about later too, I think. It can make this exact case easier to wrap your head around because you don't have to negate anything. It will run the loop once no matter what, and then check to see if the condition is true. So you could change your code to something entirely different if it's easier to follow:

boolean needValidInput = true;

do {
   // prompt for input, at least once
} while (needValidInput); // then repeat til needValidInput gets turned false

Hi Ray,

1) A while loop needs an expression which evaluates to a boolean for it to be a valid while loop, yes.

2) Yes, the while loop has to close so that the play() loop can run again and displayProgress() before re-entering the while loop of promptForGuess().

3) The catch prints out a notice to try again, but you don't need to be told how many guesses you have remaining again, so it doesn't break the while loop.

It sounds like you've got this down, unless I'm mistaken!

Thanks again Evan and Gavin, I think I am safe and confident enough to move on for now

Thanks Gavin.

I am slowly getting the hang of it, I have typed out my way of thinking it above on replying to Evan's answer, feel free to go take a look and see if I am getting closer to the answer or am I wandering further away from the right path.

Short question here, the isValidGuess is always coming out as true right? No matter where it ends up at, either in the try block or the catch block, so we would always be going through the while looop again endlessly at this point?

Ray.

Oh nono, your example is perfect, way to "Keep It Simple Stupid". So what if you set your hungry condition to false in the first place, so it makes your supposedly hungry variable becomes full, for example:

public boolean hungry = false;

while (!hungry) {
eat();
}

Does it now say while I am (!)NOT full, I eat?

Right!

You are saying:

while (the value of "hungry" is not false) {
// the condition is true
do the loop !

}

So boolean varibales in while loop has to to true in order for it to run?