FlappyTurtle/Manager.java

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;

class Manager implements KeyListener
{
    enum States
    {
        INTRO,
        GAME
    }
    private final String USAGE =
        "------------------------------\n" +
        "Simple version of Flappy Bird\n" +
        "Press SPACE to jump!\n" +
        "------------------------------\n";
    private final GameScreen _game;
    private States _state;

    public Manager()
    {
        Turtle turtle = new Turtle();
        turtle.setzeGeschwindigkeit(10);

        JFrame fieldValue = new JFrame();
        // Modifying Turtle.java is forbidden so use reflection to get the JFrame and add
        // a KeyListener lol
        try
        {

            Field frameField = TurtleWelt.class.getDeclaredField("_frame");

            frameField.setAccessible(true);

            fieldValue = (JFrame) frameField.get(TurtleWelt.globaleWelt);
            fieldValue.addKeyListener(this);
        }
        catch (Exception ex)
        {
            System.out.println("Reflection hack failed");
            System.exit(-1);
        }

        System.out.print(USAGE);

        IntroScreen intro = new IntroScreen();
        _game = new GameScreen();
        _state = States.INTRO;

        long lastNanos, elapsed;
        long total = 0;
        lastNanos = System.nanoTime();
        while (true)
        {
            elapsed = System.nanoTime() - lastNanos;
            total += elapsed;
            lastNanos = System.nanoTime();

            switch (_state)
            {
                case GAME:
                    _game.update(elapsed * 1e-6d);
                    _game.draw(turtle, elapsed * 1e-6d);
                    break;
                case INTRO:
                    intro.draw(turtle);
                    // Start game after 3 seconds
                    if (total > 3e9)
                    {
                        startGame();
                    }
                    break;
            }

            // Try to achieve approximately 60 FPS (1000ms / 60 FPS = 16.666ms)
            int missingMs = (int)(16 - (System.nanoTime() - lastNanos) * 1e-6d);
            if (missingMs > 0)
            {
                try
                {
                    Thread.sleep(missingMs);
                } catch (Exception e) {}
            }
        }
    }

    private void startGame()
    {
        _state = States.GAME;
    }

    public void keyPressed(KeyEvent e)
    {
        if (e.getKeyCode() == KeyEvent.VK_SPACE)
        {
            _game.jump();
        }
        else if (e.getKeyCode() == KeyEvent.VK_ESCAPE)
        {
            System.exit(0);
        }
    }

    public void keyReleased(KeyEvent e) {}
    public void keyTyped(KeyEvent e) {}
}