Variable Assignment and loops (Java)

Question

Greetings Stack Overflowers,

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.

(suggestions for better title and tags also appreciated)

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.

Answer 2

This is not about declaration of the variable, but about the objects you create. Arrays in java only hold references to objects, so if you actually want to have distinct objects in the array, you need to create them with new somewhere in the loop.

tempElement = new WhateverClass();

Answer 3

Element tempElement;

while(condition){
    tempElement = new HashElement();

    //do more stuff

    elementArray[index] = tempElement;
}