SimpleDraw.java

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class SimpleDraw {
    public static void main(String[] args) {
        JFrame f = new JFrame("SimpleDraw"); 
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(300, 300);                   
        f.setContentPane(new Canvas());         
        f.setVisible(true);                     
    }
}

// JComponent is a base class for custom components
class Canvas extends JComponent {
	
    Point M = new Point(); // mouse point
    Point C = new Point(150, 150); // click point

	Canvas(){
		super();
		this.addMouseListener(new MouseAdapter(){
			public void mouseClicked(MouseEvent e){
				C.x = e.getX();
				C.y = e.getY();
				repaint();
			}
		});

        this.addMouseMotionListener(new MouseAdapter(){
            public void mouseMoved(MouseEvent e){
                M.x = e.getX();
                M.y = e.getY();
                repaint();
            }
        }); 
      
	}

    // custom graphics drawing
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        // cast to get 2D drawing methods
        Graphics2D g2 = (Graphics2D) g; 

        g2.setColor(Color.BLACK);
        g2.setStroke(new BasicStroke(2));
        g2.drawLine(C.x, C.y, M.x, M.y);
        g2.fillOval(M.x - 5, M.y - 5, 10, 10);

        g2.setColor(Color.RED);
        g2.fillOval(C.x - 5, C.y - 5, 10, 10); 

        g2.drawString(String.format("%d,%d", C.x, C.y), C.x + 10, C.y + 10);       

        g2.setColor(Color.BLACK);
        g2.drawString(String.format("%d,%d", M.x, M.y), M.x + 10, M.y + 10);
    }
}