These should be protected.

src/main/java/com/gmail/nossr50/database/FlatfileDatabaseManager.java

@@ -35,7 +35,7 @@ public final class FlatfileDatabaseManager implements DatabaseManager {
     private final long UPDATE_WAIT_TIME = 600000L; // 10 minutes
     private final File usersFile;
 
-    public FlatfileDatabaseManager() {
+    protected FlatfileDatabaseManager() {
         usersFile = new File(mcMMO.getUsersFilePath());
         createDatabase();
         updateLeaderboards();

src/main/java/com/gmail/nossr50/database/SQLDatabaseManager.java

@@ -48,7 +48,7 @@ public final class SQLDatabaseManager implements DatabaseManager {
     // How many connection attempts have failed
     private int reconnectAttempt = 0;
 
-    public SQLDatabaseManager() {
+    protected SQLDatabaseManager() {
         checkConnected();
         createStructure();
     }