ArrayList error involving out of bounds exception

Question

Using edwards revised code, i now have this:

        int k, l, tempA, tempB;
    for (k = 0; k < 13; k++) {
    for (l = 0; l < 4; l++) {
    tempA = rndm.get(k);
    tempB = suit.get(l);
    // increment # and convert into string
    buttonNumber++;
    buttonName = Integer.toString(buttonNumber);
    // assign new button to the array
    cardButton[k * 4 + l] = new JButton(buttonName);
    // assign button image icon
    cardButton[k * 4 + l].setIcon(cardImage[tempA][tempB]);
    // assign value to the check variable
    check[k * 4 + l] = Integer.toString(tempA+1);
    // make button invisible for now
    cardButton[k * 4 + l].setVisible(false);
    // add the button to the board
    board.add(cardButton[k * 4 + l]);
}

}

but my problem with this is that I need a replacement for the nested loop because the way it is set up now, it displays x value in 4 different suits before displaying the next value, when what i need is for it to display x value and x suit without repeating a value once, unless done randomly. The reason this is happening is because of the nested loop which iterates through k once, and then through l four times.

Answer 1

I believe your for-loop condition is incorrect. j < 52 || k < 13 || l < 4 will return true until j >= 52. Looking at your code, this throws an out of bounds error because k and l will also increase to 52. If I were you, I'd place them in separate conditions.

It appears (according to your comment) that you want to iterate over a 2D array. In that case, I'd use 2 for-loops:

for (k = 0; k < 13; k++) {
    for (l = 0; l < 4; l++) {
        tempA = rndm.get(k);
        tempB = suit.get(l);
        cardButton[k * 4 + l].setIcon(cardImage[tempA][tempB]);
        check[k * 4 + l] = Integer.toString(tempA+1);
    }
}

Note that we're replacing your j variable with some math instead. Every time you go through your l loop, k is incremented by one. Thus, we can tell what card we're on by multiplying k by 4, since l goes through 4 times. If we add l, we can get the current card that you're looking at. This code should work right out of the box.

Edit: Your full code should be as followed.

int k, l, tempA = 0, tempB = 0;
    // create temporary variables
for (k = 0; k < 13; k++) {
    for (l = 0; l < 4; l++) {
        tempA = rndm.get(k);
        tempB = suit.get(l);
        // increment # and convert into string
        buttonNumber = buttonNumber+1;
        buttonName = Integer.toString(buttonNumber);
        // assign new button to the array
        cardButton[k * 4 + l] = new JButton(buttonName);
        // assign button image icon
        cardButton[k * 4 + l].setIcon(cardImage[tempA][tempB]);
        // assign value to the check variable
        check[k * 4 + l] = Integer.toString(tempA+1);
        // make button invisible for now
        cardButton[k * 4 + l].setVisible(false);
        // add the button to the board
        board.add(cardButton[k * 4 + l]);
    }
}

Also, instead of doing buttonNumber = buttonNumber + 1, you can use buttonNumber++

Answer 2

If you're trying to get every permutation of rndm and suit, you'll need a nested loop:

for (int i = 0; i < 13; i++) {
    for (int j = 0; j < 4; j++) {
        tempA = rndm.get(i);
        tempB = suit.get(j);
        //...
    }
}

Answer 3

You are misunderstanding how logical operators work. Double vertical bar is "or" operator. It takes two expressions that can be casted to boolean values and returns true if at least one of them is true.

boolean test = (1 == 2 || 5 < 3);
// test == true

Your for loop is iterating outside of the array bounds. Let's simplify your code a little bit. Let's create two arrays with fixed size, 1 and 2 elements, and then iterate over them in a loop similar to yours.

Integer[] arrayA = new Integer[1];
Integer[] arrayB = new Integer[2];

for (int i = 0, j = 0; i < 1 || j < 2; i++, j++) {
    arrayA[i] = i; // Will throw ArrayIndexOutOfBounds
    arrayB[j] = j;
}

Now, let's see how the counters will change during loop execution:

1. i == 0 and j == 0, i < 1 == true and j < 2 == true, we increment both
2. i == 1 and j == 1, i < 1 == false but still j < 2 == true, one of the conditions is true (and we need only one to be true in order for || operator to return true) so the loop code is executed even though i index is out of bounds!

Your code throws an exception for the same reason. Even though l < 4 == false, whole condition evaluates to true, therefore loop code will be executed.

What you want is to change all of the || operators to &&:

for (j = 0, k = 0, l = 0; j < 52 && k < 13 && l < 4; j++, k++, l++)

You can read more about boolean algebra and difference between and and or operators here - http://www.tutorialspoint.com/computer_logical_organization/boolean_algebra.htm

On a side note, don't do loops like that. So many variables in one statement are very confusing, as you might have noticed. Consider using enchanced for loops if you are always accessing objects with the exact same index as your counter variable.