Getting an instance of PlotSquared

import com.intellectualcrafters.plot.api.PlotAPI;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.plugin.PluginManager;

public class Main extends JavaPlugin {
    public PlotAPI api;

    @Override
    public void onEnable() {
        PluginManager manager = Bukkit.getServer().getPluginManager();
        final Plugin plotsquared = manager.getPlugin("PlotSquared");

        // Disable the plugin if PlotSquared is not installed

        // If you move any PlotSquared related tasks to en external class you 
        // wouldn't have to disable the plugin if PlotSquared wasn't installed

        if(plotsquared != null && !plotsquared.isEnabled()) {
            sendMessage(null, "&c[PlotApproval] Could not find PlotSquared! Disabling plugin...");
            manager.disablePlugin(this);
            return;
        }

        // Do PlotSquared related stuff
        api = new PlotAPI(this);

        // You can now use this api object to do powerful things.
    }
}