An off-topic question regarding basic Java Programming

[Itaru]

Here you go:

Code:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Paint;
import java.awt.Point;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class GradientTranslucentWindow extends JFrame implements KeyListener, MouseListener, MouseMotionListener {
    private int counter = 0;
    private int draw = 0;
    private Point start, end;
    private JPanel panel;
    private static final int red[] = {58, 71, 231, 243, 255};
    private static final int green[] = {54, 224, 235, 109, 40};
    private static final int blue[] = {241, 95, 61, 52, 40};
    private static final int R = 240;
    private static final int G = 240;
    private static final int B = 200;

    public GradientTranslucentWindow() {
        setBackground(new Color(0, 0, 0, 0));
        setSize(new Dimension(500, 500));
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        panel = new JPanel() {
            protected void paintComponent(Graphics g) {
                if (g instanceof Graphics2D) {
                    Paint p = new GradientPaint(0.0f, 0.0f, new Color(R, G, B, 50),
                            0.0f, getHeight(), new Color(R, G, B, 255), true);
                    Graphics2D g2d = (Graphics2D) g;
                    g2d.setPaint(p);
                    g2d.fillRect(0, 0, getWidth(), getHeight());
                    if (draw == 1) {
                        g2d.setColor(new Color(red[counter], green[counter], blue[counter]));
                        g2d.drawLine(start.x, start.y, end.x, end.y);
                        start = end;
                    }
                }
            }
        };
        setContentPane(panel);
        addKeyListener(this);
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    public static void main(String[] args) {
        JFrame.setDefaultLookAndFeelDecorated(true);
        new GradientTranslucentWindow().setVisible(true);
    }

    public void mousePressed(MouseEvent e) {
        start = e.getPoint();
        if (e.getButton() == MouseEvent.BUTTON1) draw = 1;
        else if (e.getButton() == MouseEvent.BUTTON3) draw = 0;
    }

    public void mouseClicked(MouseEvent e) {}

    public void mouseEntered(MouseEvent e) {}

    public void mouseExited(MouseEvent e) {}

    public void mouseReleased(MouseEvent e) {}

    public void mouseDragged(MouseEvent e) {
        start = e.getPoint();
    }

    public void mouseMoved(MouseEvent e) {
        if (draw == 1) {
            end = e.getPoint();
            int x = (start.x < end.x) ? start.x : end.x;
            int y = (start.y < end.y) ? start.y : end.y;
            panel.repaint(x, y, Math.abs(start.x - end.x) + 1, Math.abs(start.y - end.y) + 1);
            System.out.println(start.x + " - " + start.y);
        }
    }

    public void keyPressed(KeyEvent e) {
        if (e.getKeyCode() == KeyEvent.VK_SPACE) {
            counter++;
            if (counter > 4) counter = 0;    
        }
    }

    public void keyReleased(KeyEvent e) {}

    public void keyTyped(KeyEvent e) {}
}