Can this be done better with the Raster class? Or some other way?

[Paul Richards]

Hi, I have an application that creates a load of grids on a panel, they are interlinked rectangles, and portions of them have uniform size, but then there are other grids with a different size and they can have different background colours. I decided to write this method that draws one of the grids, and it does just what I want.

    /**
     * Generates an image which looks like a rectangular grid
     * @param cellWidth the width of the cells in pixels; one pixel is taken up with the border
     * @param cellHeight the height of the cells in pixels; one pixel is taken up with the border
     * @param cellsWide the number of cells across (number of columns)
     * @param cellsHigh the number of cells down (number of rows)
     * @param background the background colour
     * @return a new image meeting the requirements, drawn with black lines
     */
    public static Image GridImage(byte cellWidth, byte cellHeight, byte cellsWide, byte cellsHigh, Color background) {
        int widthPixels = cellWidth*cellsWide+1;
        int heightPixels = cellHeight*cellsHigh+1;
        BufferedImage bi = new BufferedImage(widthPixels, heightPixels, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = (Graphics2D) bi.getGraphics();
        g2d.setBackground(background);
        g2d.clearRect(0, 0, widthPixels, heightPixels);
        g2d.setColor(Color.BLACK);
        for(byte i=0; i<=cellsWide; i++) {
            int x = i*cellWidth;
            g2d.drawLine(x, 0, x, heightPixels-1);
        }
        for(byte i=0; i<=cellsHigh; i++) {
            int y = i*cellHeight;
            g2d.drawLine(0, y, widthPixels-1, y);
        }
        return bi;
    }

I have looked into the Raster class but it looks kinda complicated. Can any of you people who have experience in it tell me if it would make the above code more elegant, faster or better?

[JosAH]

Can any of you people who have experience in it tell me if it would make the above code more elegant, faster or better?

It looks fine to me; no further questions your honour ;-)

kind regards,

Jos

[quad64bit]

You could move the declaration of x and y outside the loop to prevent a lot of extra garbage collection (reassignment vs recreation) which would turn your code up one notch - to 11.

:D

[JosAH]

You could move the declaration of x and y outside the loop to prevent a lot of extra garbage collection (reassignment vs recreation) which would turn your code up one notch - to 11.

:D

Java doesn't work that way: whether or not you take those variable out of the loop they are stored on the stack and there is nothing to garbage collect for those primitives (check it with javap -c). Taking those variables out of the loop will take a bit more stack space until the end of their (larger) scope.

kind regards,

Jos

[quad64bit]

Oh really? So, if you put a declaration in a loop, it doesn't add (and then mark for garbage collection) a variable to the stack every cycle of the loop? i.e. Executing a declaration in a loop doesn't add n number of variables to the stack?

[JosAH]

Oh really? So, if you put a declaration in a loop, it doesn't add (and then mark for garbage collection) a variable to the stack every cycle of the loop? i.e. Executing a declaration in a loop doesn't add n number of variables to the stack?

Here x and y are primitives (ints) so there is nothing to be garbage collected; they exist on the stack and the stack is there (same when they were defined outside of the loop). Defining (allocating) an object variable inside of the loop (and forgetting about it at the end of the loop body) is an entirely different cup of tea; it doesn't matter for the references to it, i.e. they can be defined in the loop body without a problem.

kind regards,

Jos

[quad64bit]

Ah, good point - for some reason I wasn't thinking about the fact that they were primitive values (not objects!). Very good point, and this back and forth should prove very useful to others.

Cheers!