Boundary fill java causing stackOverflow

Question

i am trying to implement a simple application with the boundary fill algorithm in java and each time i am getting a stackoverflow error and i don't know why.

from the post i have seen, i believe it is because of the Robot.

here is the code

import java.awt.AWTException;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Robot;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

@SuppressWarnings("serial")
public class drawfill extends JPanel implements MouseListener,MouseMotionListener  {

    public static JFrame shell;
    public static Dimension shellSize = new Dimension(500, 500);
    public Graphics2D G;
    public Color boundaryColor = Color.black;
    public Color fillColor = Color.yellow;
    public int xInit;
    public int yInit;
    public int xFinal;
    public int yFinal;
    public boolean fill  = false;
    public Robot rb;
    BufferedImage img;
    Graphics2D gimg;

    public static void main(String[] args) throws AWTException {
        shell = new JFrame("Draw");
        shell.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent we){
                System.exit(0);
            }
        });
        shell.setLayout(new BorderLayout());
        shell.setMinimumSize(shellSize);
        shell.setResizable(false);
        drawfill dpanel = new drawfill();
        RadioPanelClass radio = dpanel.new RadioPanelClass();

        shell.add(radio,BorderLayout.NORTH);
        shell.add(dpanel,BorderLayout.CENTER);
        shell.setVisible(true);
        shell.setLocationRelativeTo(null);
    }

    public drawfill() throws AWTException{
        rb = new Robot();
        super.setBackground(Color.white);
        changeCursor(true);
        super.addMouseMotionListener(this);
        super.addMouseListener(this);           
    }

    public void paint(Graphics g){
        G = (Graphics2D)g;
        super.paint(G);
        G.setColor(boundaryColor);
        G.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
        G.drawRect(xInit, yInit, xFinal - xInit, yFinal - yInit);
    }

    public void changeCursor(boolean b){
        //true for draw 
        //flase for fill
        if (b)
            super.setCursor(Cursor.getPredefinedCursor (Cursor.CROSSHAIR_CURSOR));
        else
            super.setCursor(Cursor.getPredefinedCursor (Cursor.HAND_CURSOR));
    }

    public Color getPixel(int x,int y){
        return rb.getPixelColor(x,y);
    }

    public void setPixel(int x,int y,Color color){
        G.setColor(color);
        G.fillOval(x, y, 1, 1);

    }

    public void boundaryFill(int x, int y, Color fill,Color boundary) {
        Color interior = getPixel(x,y); 
        //System.out.println(interior.toString());
        if (interior != boundary && interior != fill){
            setPixel(x,y,fill);
            boundaryFill(x+1,y,fill,boundary);
            boundaryFill(x-1,y,fill,boundary);
            boundaryFill(x,y+1,fill,boundary);
            boundaryFill(x,y-1,fill,boundary);
        }
    }


    @Override
    public void mouseClicked(MouseEvent e) {
        if (fill){
            int x = e.getX();
            int y = e.getY();
            boundaryFill(x,y,fillColor,boundaryColor);
        }
    }

    @Override
    public void mouseEntered(MouseEvent e) {}

    @Override
    public void mouseExited(MouseEvent e) {}

    @Override
    public void mousePressed(MouseEvent e) {
        if (!fill){
            xInit = e.getX();
            yInit = e.getY();
        }
    }

    @Override
    public void mouseReleased(MouseEvent e) {}

    @Override
    public void mouseDragged(MouseEvent e) {
        if (!fill){
            xFinal = e.getX();
            yFinal = e.getY();
            repaint();
        }
    }

    @Override
    public void mouseMoved(MouseEvent e) {}

    class RadioPanelClass extends JPanel implements ActionListener {

        RadioPanelClass(){

            JRadioButton draw = new JRadioButton("draw");
                draw.setActionCommand("draw");
                draw.setSelected(true); 
            JRadioButton fill = new JRadioButton("fill");
                fill.setActionCommand("fill");
            super.add(draw);
            super.add(fill);

            ButtonGroup TypeRadio = new ButtonGroup();
            TypeRadio.add(draw);
            TypeRadio.add(fill);

            // Register a listener for the radio buttons.
            draw.addActionListener(this);
            fill.addActionListener(this);

        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String actionCommand = e.getActionCommand();
            if (actionCommand == "draw") {
                changeCursor(true);
            }
            else if (actionCommand == "fill"){
                changeCursor(false);
                fill = true;
            }
        }
    }
}

the Error:

Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
    at sun.nio.cs.SingleByte.withResult(Unknown Source)
    at sun.nio.cs.SingleByte.access$000(Unknown Source)
    at sun.nio.cs.SingleByte$Encoder.encodeArrayLoop(Unknown Source)
    at sun.nio.cs.SingleByte$Encoder.encodeLoop(Unknown Source)
    at java.nio.charset.CharsetEncoder.encode(Unknown Source)
    at sun.nio.cs.StreamEncoder.implWrite(Unknown Source)
    at sun.nio.cs.StreamEncoder.write(Unknown Source)
    at java.io.OutputStreamWriter.write(Unknown Source)
    at java.io.BufferedWriter.flushBuffer(Unknown Source)
    at java.io.PrintStream.write(Unknown Source)
    at java.io.PrintStream.print(Unknown Source)
    at java.io.PrintStream.println(Unknown Source)
    at test.drawfill.boundaryFill(drawfill.java:99)
    at test.drawfill.boundaryFill(drawfill.java:102)
    at test.drawfill.boundaryFill(drawfill.java:102)

UPDATE:

i tried to change the code and use BufferedImage instead but i and still getting the same stackOverFlow error here is the updated code:

public void paintComponent(Graphics g){
        G = (Graphics2D)g;
        super.paintComponent(G);
        super.setBackground(Color.white);
        bi = new BufferedImage(super.getWidth(),super.getHeight(),BufferedImage.TYPE_INT_RGB);
        gbi = bi.createGraphics();

        gbi.setBackground(Color.WHITE);
        gbi.clearRect(0,0,super.getWidth(),super.getHeight());
        gbi.setColor(boundaryColor);
        gbi.drawRect(xInit, yInit, xFinal - xInit, yFinal - yInit);
        G.drawImage(bi, 0,0,null);
        gbi.dispose();
    }

public Color getPixel(int x,int y){
        return new Color(bi.getRGB(x, y));
    }

    public void setPixel(int x,int y,Color color){
        bi.setRGB(x, y, color.getRGB());
        repaint();
    }

    public void boundaryFill(int x, int y, Color fill,Color boundary) {
        if ( (x>= xInit && x<= xFinal) && (y>= yInit && y<=yFinal) ){
            Color interior = getPixel(x,y); 
            //System.out.println(interior.toString());
            if (interior != boundary && interior != fill){
                setPixel(x,y,fill);
                boundaryFill(x+1,y,fill,boundary);
                boundaryFill(x-1,y,fill,boundary);
                boundaryFill(x,y+1,fill,boundary);
                boundaryFill(x,y-1,fill,boundary);
            }
            else
                return;
        }
        else
            return;
    }

Answer 1

You are using rb to determine the color of a given pixel, which is supposed to be controlling the recursion of boundaryFill. But when you set a pixel, you manipulate G, and it is not clear if (much less how) rb is being informed of these pixel changes; if rb never changes, then there is nothing to stop the recursion of boundaryFill.

Answer 2

There are several problems here that are combining:

As Scott Hunter's answer suggests, a java.awt.Robot operates on the actual color of pixels on the screen, not on the colors in the Graphics2D. This means that the color returned by Robot.getPixelColor(screenX, screenY) won't be updated until the Graphics2D is actually painted to the screen - which can't happen in the middle of your boundaryFill() call.

Additionally, a Robot operates in screen coordinates, while the Graphics2D is operating in the coordinate space of (in this case) your JPanel - meaning that even if you did repaint, the arguments to Robot.getPixelColor would need to be different than the arguments to G.fillOval.

Next, you're not doing bounds checking on the coordinates passed to boundaryFill() - meaning that if your recursion ever hits the edge of the area, you'll keep recursing until x is Integer.MAX_VALUE or your stack overflows.

As an additional bonus, I'd have to double check, but I'm pretty sure holding on to the Graphics2D that's passed in to Component.paint() is not likely to be well-behaved. The traditional way to do what you're trying would be to create a BufferedImage offscreen, render into it, and then call Graphics2D.drawImage() in your paintComponent() override. (Since you're extending JPanel and therefore using Swing, you should be overriding paintComponent instead of paint anyway. Doing this would also let you avoid using the Robot, since you can use BufferedImage.getRGB to determine pixel colors.

Answer 3

I have already answered this: https://stackoverflow.com/a/67253198/8196026

You are giving larger dimensions of your figure than what it could handle that's why recurring calls and recursion stack gets out of memory, like here its 500 in your case. I suggest try reducing this dimension and it should work fine.