Question

I want to make an application in which I can draw a path on a canvas. The problem is that I have to update this canvas continuously.

Currently I’m able to do it, but I have to redraw all the path every time and so I have to store all the points in memory. I would prefer to simply update the draw by adding a new point.

Is it possible?

Currently my code is:

public class MyCanvas extends Canvas{
        private static final long serialVersionUID = 1L;
        public MyCanvas(){}
        public void paint(Graphics graphics){
            super.paint(graphics);
            graphics.setColor(Color.green);
            // points is an ArrayList of Point2D
            for (Iterator iterator = points.iterator(); iterator.hasNext();) {
               Point2D point2d = (Point2D) iterator.next();
               graphics.fillOval((int)((canvas.getWidth()/2.0) + point2d.getX()), (int)((canvas.getHeight()/2.0) + point2d.getY()), 5, 5);
            }   
        }
    }

Thanks!

EDIT

This is the current solution:

PanelCanvas canvasPanel;
...
public void drawCircle(int x, int y){
    Graphics2D g2d = bufferedImage.createGraphics();
    g2d.setColor(Color.green);
    g2d.setBackground(Color.white);
    g2d.fillOval((int)((panelCanvas.getWidth() / 2.0) + x/10.0), (int)((panelCanvas.getHeight() / 2.0) + y/10.0), 5, 5);
    panelCanvas.repaint();
}

public class CanvasPanel extends JPanel{
    public void paintComponent(Graphics graphics){
        super.paintComponents(graphics);
        Graphics2D g2d = (Graphics2D)graphics;
        g2d.setBackground(Color.white);
        g2d.drawImage(bufferedImage, null, 0, 0);
    }
}

Answer 1

Draw the points (whatever) to a BufferedImage. During paint(), draw the BufferedImage.

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Note though, that the JRE can draw thousands of objects in paint without any visual artifacts or slow-down.

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The canvas is embedded in a Swing GUI. What do you suggest for replacing AWT.Canvas?

JComponent for complete custom rendering, JPanel for custom rendering combined with components. It sounds like the JComponent would be better suited to this use-case.

For either of those, override paintComponent(Graphics) instead of paint(Graphics). The rest of the advice is the same.