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

import java.awt.event.*;
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Main extends JPanel {
    private static final int DEFAULT_WIDTH = 800;
    private static final int DEFAULT_HEIGHT = 800;
    private static final Color BACK_COLOR = Color.WHITE;
    private Color curColor = Color.BLACK;

    private int x1, y1, x2, y2;
    private Graphics g;


    public static void main(String[] args) {
        JFrame frame = new JFrame("Paint program simple");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        JPanel panel = new Main();
        frame.add(panel);

        frame.pack();
        frame.setVisible(true);
    }


    private Main() {
        setBackground(BACK_COLOR);
        setPreferredSize(new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT));

        MyMouseHandler handler = new MyMouseHandler();

        this.addMouseListener(handler);
        this.addMouseMotionListener(handler);
        this.setFocusable(true);
        this.addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                // TODO Auto-generated method stub
                int key = e.getKeyCode();
                switch (key) {
                    case KeyEvent.VK_Y:
                        curColor = Color.YELLOW;
                        break;
                    case KeyEvent.VK_R:
                        curColor = Color.RED;
                        break;
                    case KeyEvent.VK_G:
                        curColor = Color.GREEN;
                        break;
                    case KeyEvent.VK_O:
                        curColor = Color.ORANGE;
                        break;
                    case KeyEvent.VK_B:
                        curColor = Color.BLACK;
                        break;
                }
            }
        });
    }

    private class MyMouseHandler extends MouseAdapter {
        public void mousePressed(MouseEvent e) {
            x1 = e.getX();
            y1 = e.getY();

            g = getGraphics();

            x2 = x1;
            y2 = y1;
        }

        public void mouseDragged(MouseEvent e) {
            x1 = e.getX();
            y1 = e.getY();

            g.setColor(curColor);
            g.drawLine(x1, y1, x2, y2);

            x2 = x1;
            y2 = y1;
        }
    }}