Complete box? drawing lines

Question

Hello,
I want to allow a user to draw lines on a canvas and then know when all the points make up an area that is a box.
How can this be done? What checks would I need to do everytime a line is drawn?

Answer 1

A few fixes:
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class ClickHere extends JPanel {
    private GeneralPath path;
    private int startX=-1, startY=-1;
    private Color foreground = Color.RED;
    public ClickHere() {
        addMouseListener(new MouseAdapter(){
            public void mousePressed(MouseEvent evt) {
                int x = ((evt.getX()+5)/10)*10;
                int y = ((evt.getY()+5)/10)*10;
                if (path == null) {
                    path = new GeneralPath();
                    path.moveTo(x, y);
                    startX = x;
                    startY = y;
                } else if (x==startX && y == startY) {
                    path.closePath();
                    foreground = Color.GREEN;
                    removeMouseListener(this);
                } else
                    path.lineTo(x, y);
                repaint();
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (path != null) {
            Graphics2D g2 = (Graphics2D) g;
            g2.setColor(foreground);
            g2.drawRect(startX-2, startY-2, 5, 5);
            g2.draw(path);
    public static void main(String[] args) {
        JFrame f = new JFrame("ClickHere");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new ClickHere());
        f.setSize(450, 400);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
}