This should be private.

src/main/java/com/gmail/nossr50/commands/general/XprateCommand.java

@@ -14,7 +14,7 @@ import com.gmail.nossr50.util.Misc;
 public class XprateCommand implements CommandExecutor {
     private final mcMMO plugin;
     private static int oldrate = Config.getInstance().xpGainMultiplier;
-    public static boolean xpevent = false;
+    private static boolean xpevent = false;
 
     public XprateCommand (mcMMO plugin) {
         this.plugin = plugin;
@@ -90,4 +90,8 @@ public class XprateCommand implements CommandExecutor {
             return true;
         }
     }
+
+    public static boolean isXpEventRunning() {
+        return xpevent;
+    }
 }

src/main/java/com/gmail/nossr50/listeners/PlayerListener.java

@@ -183,7 +183,7 @@ public class PlayerListener implements Listener {
         }
 
         //THIS IS VERY BAD WAY TO DO THINGS, NEED BETTER WAY
-        if (XprateCommand.xpevent) {
+        if (XprateCommand.isXpEventRunning()) {
             player.sendMessage(LocaleLoader.getString("XPRate.Event", new Object[] {Config.getInstance().xpGainMultiplier}));
         }
     }