Question

I’m working on some beginning Java logic, and I’m not sure why this is not working. Here is a method I made:

private void printSubclassBoxes(){
        int  coordinateX = ((getWidth() - BOX_WIDTH) /4);

        for ( int i = 0; i < 3; i++){

            double coordinateY = (getHeight() / 2);     
            GRect classBox = new GRect (coordinateX, coordinateY, BOX_WIDTH, BOX_HEIGHT);

            GLabel classLabel = new GLabel ("Program");
            double labelCoordinateX = (coordinateX + ((classBox.getWidth() / 2) - (classLabel.getWidth() / 2)));
            double labelCoordinateY = (coordinateY + ((classBox.getHeight() / 2) + (classLabel.getAscent() / 2)));
            add(classBox);
            add(classLabel, labelCoordinateX, labelCoordinateY);
            if (i == 1){
            coordinateX = (((getWidth() - BOX_WIDTH) /4) * 2);
        } 
        if (i == 2){
            coordinateX = (((getWidth() - BOX_WIDTH) /4) * 3);
        } 

        }   

    }

Now I’m sure there are probably better ways to do this, but please-I’m not interested in that right now (I’m trying to learn without being spoonfed the answers). All I am wanting to know is why the ending two if statements are not working like I think they should.

For simplicity sake, let’s say

100 = ((getWidth() - BOX_WIDTH)

int coordinateX = 25;

My understanding is that int i gets to that first if statement and adds 25 + 25 so then coordinateX = 50.

then next time in the loop, i = 2 so coordinateX would = 75.

This is what I’m expecting to happen, but it’s not. I seem to be printing the first two boxes directly on top of each other, and then the third is moving 25.

Thanks for your help guys. Now that I got that loop figured out, I went ahead and solved it a different way. I ended up assigning coordinateX to another variable and using that to add to the end:

int  coordinateX = ((getWidth() - BOX_WIDTH) /4);
        int otherCoordinateX = coordinateX;

        for ( int i = 0; i < 3; i++){

            double coordinateY = (getHeight() / 2);     
            GRect classBox = new GRect (coordinateX, coordinateY, BOX_WIDTH, BOX_HEIGHT);

            GLabel classLabel = new GLabel ("Program");
            double labelCoordinateX = (coordinateX + ((classBox.getWidth() / 2) - (classLabel.getWidth() / 2)));
            double labelCoordinateY = (coordinateY + ((classBox.getHeight() / 2) + (classLabel.getAscent() / 2)));
            add(classBox);
            add(classLabel, labelCoordinateX, labelCoordinateY);
            coordinateX = otherCoordinateX + coordinateX;

        }   

Answer 1

at the first iteration of the loop:

• i = 0, and
• coordinateX = 25, as expected.

At the end of the iteration coordinateX is not updated (since i == 0).

Then, at the second iteration:

• i = 1,
• but still coordinateX = 25 since it wasn’t updated.

At the end of the second iteration coordinateX is updated because of the if i == 1) test.

In the third iteration

• i = 2
• the new value of coordinateX is used, which was set at the end of the second iteration.

Solution

To not change your code in any essential way, simply replace if (i == 1) by if (i == 0), and if (i == 2) by if (i == 1).

EDIT: Lesson

In the for(...) { } declaration, the i < 3 test is checked at the beginning of each iteration, but the i++ part is called at the end of each iteration.