Question

A while back, I was working on a program that hashed values into a hashtable (I don’t remember the specifics, and the specifics themselves are irrelevant to the question at hand). Anyway, I had the following code as part of a “recordInput” method:

tempElement = new hashElement(someInt);

    while(in.hasNext() == true)
    {
        int firstVal = in.nextInt();
        if (firstVal == -911)
        {
            break;
        }
        tempElement.setKeyValue(firstVal, 0);
        for(int i = 1; i<numKeyValues;i++)
        {
            tempElement.setKeyValue(in.nextInt(), i);
        }

        elementArray[placeValue] = tempElement;
        placeValue++;

    }   // close while loop

} // close method

This part of the code was giving me a very nasty bug — no matter how I finagled it, no matter what input I gave the program, it would always produce an array full of only a single value — the last one.

The problem, as I later determined it, was that because I had not created the tempElement variable within the loop, and because values were not being assigned to elementArray[] until after the loop had ended — every term was defined rather as “tempElement” — when the loop terminated, every slot in the array was filled with the last value tempElement had taken.

I was able to fix this bug by moving the declaration of tempElement within the while loop. My question to you, Stackoverflow, is whether there is another (read: better) way to avoid this bug while keeping the variable declaration of tempElement outside the while loop.

Answer 1

Why would you want to keep the variable declaration outside the while loop? Anyway, you can, as long as you assign it to a new hashElement each time:

hashElement tempElement;
while (/*...*/) {
    tempElement = new hashElement();
    //...

It’s certainly not “better” though. Scope your variables as narrowly as possible, in general.