// Studscanvas.java

import java.util.*;
import javax.microedition.lcdui.*;

public class Studscanvas extends Canvas {
    int ball_radius;
    double ball_x, ball_y, ball_dx, ball_dy;
    Timer the_timer;

    public Studscanvas() {
        int screen_width = getWidth();
        int screen_height = getHeight();

        ball_radius = 5;
        ball_x = screen_width / 2;
        ball_y = screen_height / 2;
        ball_dx = 1;
        ball_dy = -1;
    }

    public void showNotify() {
        the_timer = new Timer();
        TimerTask task = new TimerTask() {
                public void run() {
                    update_game_state();
                    repaint();
                }
            };
        the_timer.schedule(task, 0, 20);
    }

    public void hideNotify() {
        if (the_timer != null) {
            the_timer.cancel();
            the_timer = null;
        }
    }

    private void update_game_state() {
        int screen_width = getWidth();
        int screen_height = getHeight();
        ball_x += ball_dx;
        ball_y += ball_dy;
        if (ball_x + ball_radius >= screen_width) {
            ball_dx *= -1;
        }
        else if (ball_x - ball_radius <= 0) {
            ball_dx *= -1;
        }
        if (ball_y - ball_radius <= 0) {
            ball_dy *= -1;
        }
        else if (ball_y + ball_radius >= screen_height) {
            ball_dy *= -1;
        }

        System.out.println("ball_x = " + ball_x + ", ball_y = " + ball_y +
                           ", ball_dx = " + ball_dx + " + ball_dy = " + ball_dy);
    }

    public void paint(Graphics g) {
        g.setColor(0xffffff);
        g.fillRect(0, 0, getWidth(), getHeight());
        g.setColor(0x000000);
        g.fillArc((int)(ball_x - ball_radius), (int)(ball_y - ball_radius),
                  ball_radius * 2, ball_radius * 2, 0, 360);
    }

} // class Studscanvas