import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JPanel;

class MyCurve{
    Color color;
    ArrayList<Integer> ptx;
    ArrayList<Integer> pty;
    MyCurve(){
        ptx = new ArrayList<>();
        pty = new ArrayList<>();

        int r = (int)(Math.random()*256);
        int g = (int)(Math.random()*256);
        int b = (int)(Math.random()*256);
        color = new Color(r,g,b);
    }
    void addPoint(int x, int y) {
        ptx.add(x);
        pty.add(y);
    }
    void draw(Graphics g)   {
        g.setColor(color);
        for(int i=0; i<ptx.size()-1; i++) {
            int x1 = ptx.get(i);
            int y1 = pty.get(i);
            int x2 = ptx.get(i+1);
            int y2 = pty.get(i+1);
            g.drawLine(x1,y1, x2, y2);
        }
    }

}

class MyGraphics2DPanel extends JPanel
                        implements MouseMotionListener,
                                   MouseListener
{
    ArrayList <MyCurve> curves;

    MyGraphics2DPanel(){
        setBackground(Color.GREEN);
        addMouseMotionListener(this);
        addMouseListener(this);
        curves = new ArrayList<>();
    }
    @Override
    public void paintComponent(Graphics g){
        super.paintComponent(g);

        for(MyCurve c : curves){
            c.draw(g);
        }
    }
    public void mousePressed(MouseEvent e) {
        MyCurve c = new MyCurve();
        c.addPoint(e.getX(), e.getY());
        curves.add(c);
    }
    public void mouseDragged(MouseEvent e) {
        if(curves.size()<1) return;
        curves.get(curves.size()-1).addPoint(e.getX(), e.getY());
        repaint();
    }
    public void mouseReleased(MouseEvent e) {
        if(curves.size()<1) return;
        curves.get(curves.size()-1).addPoint(e.getX(), e.getY());
        repaint();
    }

    public void mouseMoved(MouseEvent e) {  }
    public void mouseClicked(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
}
public class SwingGraphics2D extends JFrame{
    public static void main(String[] args) {
        new SwingGraphics2D();
    }
    SwingGraphics2D()   {
        setSize(400,400);
        setTitle("Graphics2D");

        add(new MyGraphics2DPanel());

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
    }

}