diff --git a/src/main/java/io/github/yezhihao/protostar/schema/CollectionSchema.java b/src/main/java/io/github/yezhihao/protostar/schema/CollectionSchema.java
index 748ba74..e20fc67 100644
--- a/src/main/java/io/github/yezhihao/protostar/schema/CollectionSchema.java
+++ b/src/main/java/io/github/yezhihao/protostar/schema/CollectionSchema.java
@@ -1,7 +1,7 @@
 package io.github.yezhihao.protostar.schema;
 
-import io.netty.buffer.ByteBuf;
 import io.github.yezhihao.protostar.Schema;
+import io.netty.buffer.ByteBuf;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -10,13 +10,14 @@ import java.util.Map;
 
 public class CollectionSchema<T> implements Schema<List<T>> {
 
-    private static volatile Map<Schema, CollectionSchema> cache = new HashMap<>();
+    private static volatile Map<Object, CollectionSchema> cache = new HashMap<>();
 
     public static Schema<List> getInstance(Schema schema) {
-        CollectionSchema instance = cache.get(schema);
-        if (instance == null) {
+        Object key = schema;
+        CollectionSchema instance;
+        if ((instance = cache.get(key)) == null) {
             synchronized (cache) {
-                if (instance == null) {
+                if ((instance = cache.get(key)) == null) {
                     instance = new CollectionSchema(schema);
                     cache.put(schema, instance);
                     log.debug("new CollectionSchema({})", schema);
diff --git a/src/main/java/io/github/yezhihao/protostar/schema/ConvertSchema.java b/src/main/java/io/github/yezhihao/protostar/schema/ConvertSchema.java
index 24dccfb..aeb4b12 100644
--- a/src/main/java/io/github/yezhihao/protostar/schema/ConvertSchema.java
+++ b/src/main/java/io/github/yezhihao/protostar/schema/ConvertSchema.java
@@ -1,8 +1,8 @@
 package io.github.yezhihao.protostar.schema;
 
-import io.netty.buffer.ByteBuf;
-import io.github.yezhihao.protostar.converter.Converter;
 import io.github.yezhihao.protostar.Schema;
+import io.github.yezhihao.protostar.converter.Converter;
+import io.netty.buffer.ByteBuf;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -12,18 +12,18 @@ import java.util.Map;
  */
 public class ConvertSchema<T> implements Schema<T> {
 
-    private static volatile Map<String, ConvertSchema> cache = new HashMap<>();
+    private static volatile Map<Object, ConvertSchema> cache = new HashMap<>();
 
     public static Schema getInstance(Class<? extends Converter> clazz) {
-        String name = clazz.getName();
-        ConvertSchema instance = cache.get(name);
-        if (instance == null) {
+        String key = clazz.getName();
+        ConvertSchema instance;
+        if ((instance = cache.get(key)) == null) {
             synchronized (cache) {
-                if (instance == null) {
+                if ((instance = cache.get(key)) == null) {
                     try {
                         Converter converter = clazz.newInstance();
                         instance = new ConvertSchema(converter);
-                        cache.put(name, instance);
+                        cache.put(key, instance);
                         log.debug("new ConvertSchema({})", clazz);
                     } catch (Exception e) {
                         throw new RuntimeException(e);
diff --git a/src/main/java/io/github/yezhihao/protostar/schema/ObjectSchema.java b/src/main/java/io/github/yezhihao/protostar/schema/ObjectSchema.java
index 914b5ea..599469d 100644
--- a/src/main/java/io/github/yezhihao/protostar/schema/ObjectSchema.java
+++ b/src/main/java/io/github/yezhihao/protostar/schema/ObjectSchema.java
@@ -1,20 +1,21 @@
 package io.github.yezhihao.protostar.schema;
 
-import io.netty.buffer.ByteBuf;
 import io.github.yezhihao.protostar.Schema;
+import io.netty.buffer.ByteBuf;
 
 import java.util.HashMap;
 import java.util.Map;
 
 public class ObjectSchema<T> implements Schema<T> {
 
-    private static volatile Map<Schema, ObjectSchema> cache = new HashMap<>();
+    private static volatile Map<Object, ObjectSchema> cache = new HashMap<>();
 
     public static Schema getInstance(Schema schema) {
-        ObjectSchema instance = cache.get(schema);
-        if (instance == null) {
+        Object key = schema;
+        ObjectSchema instance;
+        if ((instance = cache.get(key)) == null) {
             synchronized (cache) {
-                if (instance == null) {
+                if ((instance = cache.get(key)) == null) {
                     instance = new ObjectSchema(schema);
                     cache.put(schema, instance);
                     log.debug("new ObjectSchema({})", schema);
diff --git a/src/main/java/io/github/yezhihao/protostar/schema/StringSchema.java b/src/main/java/io/github/yezhihao/protostar/schema/StringSchema.java
index 09f1013..6e4a0d8 100644
--- a/src/main/java/io/github/yezhihao/protostar/schema/StringSchema.java
+++ b/src/main/java/io/github/yezhihao/protostar/schema/StringSchema.java
@@ -1,8 +1,8 @@
 package io.github.yezhihao.protostar.schema;
 
-import io.netty.buffer.ByteBuf;
 import io.github.yezhihao.protostar.Schema;
 import io.github.yezhihao.protostar.util.Bcd;
+import io.netty.buffer.ByteBuf;
 
 import java.nio.charset.Charset;
 import java.util.Arrays;
@@ -12,15 +12,15 @@ import java.util.Map;
 public class StringSchema {
 
     public static class Chars implements Schema<String> {
-        private static volatile Map<String, Chars> cache = new HashMap<>();
+        private static volatile Map<Object, Chars> cache = new HashMap<>();
 
         public static Schema<String> getInstance(byte pad, String charset) {
             charset = charset.toLowerCase();
             String key = new StringBuilder(10).append((char) pad).append('/').append(charset).toString();
-            Chars instance = cache.get(key);
-            if (instance == null) {
+            Chars instance;
+            if ((instance = cache.get(key)) == null) {
                 synchronized (cache) {
-                    if (instance == null) {
+                    if ((instance = cache.get(key)) == null) {
                         instance = new Chars(pad, charset);
                         cache.put(key, instance);
                         log.debug("new StringSchema({},{})", pad, charset);