Example Bukkit Event

@EventHandler // Tells the server you're working with the event handler.
public void onJump(PlayerJumpEvent event) { // Creating a new method using the PlayerJumpEvent as the 'event'.
    Player player = event.getPlayer(); // Tells the server what a 'player' is.
    player.setHealth(20.0); // Health is divided by two. (which makes it into hearts)
}