diff --git a/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java b/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java
index e9dc852..42bdabf 100644
--- a/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java
+++ b/src/main/java/org/ntlab/citrusserver/repositories/PublicBookManager.java
@@ -4,6 +4,8 @@
 import org.ntlab.citrusserver.entities.Book;
 
 import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
 
 public class PublicBookManager implements IBookListener{
 
@@ -39,6 +41,8 @@
 
     @Override
     public void bookChanged(Account account, Book book) {
+
+
     }