diff --git a/src/main/java/com/reandroid/arsc/group/EntryGroup.java b/src/main/java/com/reandroid/arsc/group/EntryGroup.java
index 833a3f7..872fc95 100755
--- a/src/main/java/com/reandroid/arsc/group/EntryGroup.java
+++ b/src/main/java/com/reandroid/arsc/group/EntryGroup.java
@@ -29,7 +29,7 @@ import java.util.Iterator;
 public class EntryGroup extends ItemGroup<Entry> {
     private final int resourceId;
     public EntryGroup(int resId) {
-        super(create(), String.format("0x%08x", resId));
+        super(ARRAY_CREATOR, String.valueOf(resId));
         this.resourceId=resId;
     }
     public int getResourceId(){
@@ -220,6 +220,10 @@ public class EntryGroup extends ItemGroup<Entry> {
         return packageBlock.getSpecStringPool();
     }
     @Override
+    public int hashCode(){
+        return resourceId;
+    }
+    @Override
     public String toString(){
         Entry entry =pickOne();
         if(entry ==null){
@@ -227,18 +231,17 @@ public class EntryGroup extends ItemGroup<Entry> {
         }
         return super.toString()+"{"+ entry.toString()+"}";
     }
-    private static BlockArrayCreator<Entry> create(){
-        return new BlockArrayCreator<Entry>(){
-            @Override
-            public Entry newInstance() {
-                return new Entry();
-            }
 
-            @Override
-            public Entry[] newInstance(int len) {
-                return new Entry[len];
-            }
-        };
-    }
+    private static final BlockArrayCreator<Entry> ARRAY_CREATOR = new BlockArrayCreator<Entry>(){
+        @Override
+        public Entry newInstance() {
+            return new Entry();
+        }
+
+        @Override
+        public Entry[] newInstance(int len) {
+            return new Entry[len];
+        }
+    };
 
 }
diff --git a/src/main/java/com/reandroid/arsc/group/ItemGroup.java b/src/main/java/com/reandroid/arsc/group/ItemGroup.java
index eab4fa9..83b3ac9 100755
--- a/src/main/java/com/reandroid/arsc/group/ItemGroup.java
+++ b/src/main/java/com/reandroid/arsc/group/ItemGroup.java
@@ -27,12 +27,10 @@ import java.util.Objects;
     private final BlockArrayCreator<T> mBlockArrayCreator;
     private final String name;
     private T[] items;
-    private final int hashCode;
     public ItemGroup(BlockArrayCreator<T> blockArrayCreator, String name){
         this.mBlockArrayCreator=blockArrayCreator;
         this.name=name;
         this.items=blockArrayCreator.newInstance(0);
-        this.hashCode = Objects.hash(getClass(), name);
     }
     public Iterator<T> iterator(){
         return iterator(false);
@@ -139,12 +137,12 @@ import java.util.Objects;
     }
     @Override
     public int hashCode(){
-        return hashCode;
+        return 31 * name.hashCode();
     }
     @Override
     public boolean equals(Object obj){
         if(obj instanceof StringGroup){
-            return hashCode==obj.hashCode();
+            return hashCode()==obj.hashCode();
         }
         return false;
     }
diff --git a/src/main/java/com/reandroid/arsc/item/StringItem.java b/src/main/java/com/reandroid/arsc/item/StringItem.java
index 8d2e825..390917a 100755
--- a/src/main/java/com/reandroid/arsc/item/StringItem.java
+++ b/src/main/java/com/reandroid/arsc/item/StringItem.java
@@ -28,18 +28,16 @@ import java.nio.CharBuffer;
 import java.nio.charset.CharacterCodingException;
 import java.nio.charset.CharsetDecoder;
 import java.nio.charset.StandardCharsets;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.List;
+import java.util.*;
 
 public class StringItem extends BlockItem implements JSONConvert<JSONObject> {
     private String mCache;
     private boolean mUtf8;
-    private final List<ReferenceItem> mReferencedList;
+    private final Set<ReferenceItem> mReferencedList;
     public StringItem(boolean utf8) {
         super(0);
         this.mUtf8=utf8;
-        this.mReferencedList=new ArrayList<>();
+        this.mReferencedList = new HashSet<>();
     }
     public boolean removeReference(ReferenceItem ref){
         return mReferencedList.remove(ref);
@@ -53,7 +51,7 @@ public class StringItem extends BlockItem implements JSONConvert<JSONObject> {
     public boolean hasReference(){
         return mReferencedList.size()>0;
     }
-    public List<ReferenceItem> getReferencedList(){
+    public Collection<ReferenceItem> getReferencedList(){
         return mReferencedList;
     }
     public void addReference(ReferenceItem ref){
@@ -62,7 +60,7 @@ public class StringItem extends BlockItem implements JSONConvert<JSONObject> {
         }
     }
     public void addReferenceIfAbsent(ReferenceItem ref){
-        if(ref!=null && !mReferencedList.contains(ref)){
+        if(ref!=null){
             mReferencedList.add(ref);
         }
     }