Single Line Chart example

SingleLineChart.java

@Override
public void onEnable() {
    Metrics metrics = new Metrics(this);
    metrics.addCustomChart(new SingleLineChart("players", new Callable<Integer>() {
        @Override
        public Integer call() throws Exception {
            // (This is useless as there is already a player chart by default.)
            return Bukkit.getOnlinePlayers().size();
        }
    }));
}
// If you use the Copy & Paste Metrics classes, use `Metrics.SingleLineChart` instead