Question

Here’s my code:

class Ramka extends JFrame
    {
    public static final int SZEROKOSC = 800;
    public static final int WYSOKOSC = 600;
    Container powZawartosci = getContentPane();
    public Ramka()
        {
        setSize(SZEROKOSC, WYSOKOSC);
        setTitle("Siatka bryły by Paweł Mysior");
        }
    public void addRectangle(int startX, int startY, int sizeX)
        {
        drawRectangle rect = new drawRectangle(startX, startY, sizeX);
        powZawartosci.add(rect);
        }  

class drawRectangle extends JPanel
    {
    private int a, startX, startY;
    public drawRectangle(int startX, int startY, int a) // square
        {
        this.a = a;
        this.startX = startX;
        this.startY = startY;
        }
    public void paintComponent(Graphics g)
        {
        Rectangle2D rect = new Rectangle2D.Double(startX, startY, a, a);
        Graphics2D g1 = (Graphics2D) g;
        g1.draw(rect);
        }
    }

public class Main
    {
    public static void main(String[] args)
        {
        Ramka ramka = new Ramka();
        ramka.addRectangle(200, 200, 50);
        ramka.addRectangle(100, 100, 100);
        ramka.addRectangle(300, 300, 150);
        ramka.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ramka.setVisible(true);
        }
    }

What I want it to do is draw three rectangles (set aside the functionality and sense of doing so, I’m still just learning).

But it draws only the last one, starting at 300 and 300. I don’t really understand the paintComponent thing…

Thanks in advance for any help,
Paul

Answer 1

I beleive that you are adding three JPanels on top of each other. This seems like an odd way to draw rectangles, but with this design, you need to use a LayoutManager.

Check out this link, and try to learn. The code below should do the trick though.

...
Container powZawartosci = getContentPane();
public Ramka()
    {
    setSize(SZEROKOSC, WYSOKOSC);
    setTitle("Siatka bryły by Paweł Mysior");
    setLayout(new BoxLayout(this, BoxLayout.LINE_AXIS));//Only this line is inserted.
    }
public void addRectangle(int startX, int startY, int sizeX)
    {
    drawRectangle rect = new drawRectangle(startX, startY, sizeX);
    powZawartosci.add(rect);
    }  
...

---

In your JPanel derivative, you can keep track of the Rectangles that you need to draw. I am writing the code below spontanously, so check for errors first.

class RectangleDrawer extends JPanel{
    ArrayList<Rectangle> rList = new ArrayList()<Rectangle>;
    public void addRectangle(Rectangle rect){
        rList.add(rect);
    }
    public void paintComponent(Graphics g){
        super.paintComponent(g);
        for(int i=0; i<rList.size(); r++){
            g.drawRectangle(rList.get(i));
        }
    }
}