Java-instanceof

Question

First off all, I made a "Game-Renderer".

My problem is that, when I need to draw the current Element: I need to know if it's a Rectangle, Circle, or an Image and so on.

My Classes (Rectangle, Circle,...) are extending from Graphic.

public class Rectangle extends Graphic {...}

And if I want to draw them I look in the List ArrayList<Graphic>

for(index = 0;index < graphicObjects.size();index++){
    currentElement = graphicObjects.get(index);

    if(currentElement instanceof Rectangle) { // Here is an error.
    Rectangle r = (Rectangle) currentElement;
    // here the drawing.
    }
}

Thanks for helping (Goggle wasn't helpful) :)

Edit:

Error is: "Incompatible conditional operand types Graphic and Rectangle"

And why I need to know the type: My code:

public static Image getImage(Graphics g,int width, int height) {
    int imgWidth = width;
    int imgHeight = height;
    BufferedImage bfImage = new BufferedImage(imgWidth, imgHeight, BufferedImage.TYPE_INT_ARGB);
    Graphics graphics = bfImage.getGraphics();

    for (int index = 0; index < grObjList.size(); index++) {
        Graphic gr = grObjList.get(index);
        if(gr instanceof Rectangle){
            graphics.setColor(gr.color);
            graphics.fillRect(gr.x, gr.y, gr.width, gr.height);
        }
    }
    return bufferedImagetoImage(bfImage);
}

Answer 1

To avoid using instanceOf , have Graphic implement an abstract draw method. Then, override draw in your Rectangle , Circle , etc classes. Then you can do

for(index = 0;index < graphicObjects.size();index++){
    currentElement = graphicObjects.get(index);
    currentElement.draw();
}

Answer 2

You are getting an error because you are trying to say that the supertype Graphic is a Rectangle which is not a Rectangle is a Graphic.

So make sure you have a function in the super type and override it in the subtypes so you dont need to do any casting.