Bukkit

This plugin offers an API for scoreboards. Here is a simple example how to use it. This example will display the join-count for players on the server (it does not save it to a database, so it will be reset each time the server restarts).

public class TestScoreboard extends JavaPlugin implements Listener
{
    private ScoreboardManger scoreboardManger;

    private Objective playerJoins;

    @Override
    public void onEnable()
    {
        scoreboardManger = getServer().getServicesManager().getRegistration(ScoreboardManger.class).getProvider();
        playerJoins = scoreboardManger.createObjective("joins", "Joins");
        getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler
    public void onJoin(PlayerJoinEvent e)
    {
        Player p = e.getPlayer();
        Integer oldCount = playerJoins.getValue(p.getName());
        playerJoins.updateScore(p.getName(), (oldCount != null ? oldCount : 0) + 1);
        PlayerScoreboard scoreboard = scoreboardManger.getScoreboard(p);
        if (scoreboard != null)
        {
            scoreboard.addObjective(playerJoins, ObjectiveDisplayPosition.SIDEBAR, 100);
        }
    }
}

Some important points:

• You will have to add something like depend: [PVPStatsScoreboard] or softdepend: [PVPStatsScoreboard] to you plugin.yml.
• Get the scoreboard bei using the ServicesManager.
• Always check, if a PlayerScoreboard is not null. It may be null if a Player has already disconnected.
• Do not add more than 15 entries to an Objective that is shown in the SIDEBAR, or Minecraft will not display anything. This is a Minecraft client limitation.
• When you call PlayerScoreboard.addObjective or PlayerScoreboard.setObjectiveDisplay you will have to specify the display priority. Only the objective with the highest priority will be displayed at a given time. So if you want switching objectives you will have to modify the priority or remove the objective and readd it later.
• Objectives are not saved. You will have to recreate them on every server start.
• PlayerScoreboard will reset when the Player disconnects. You will have to add the objectives on rejoin.