StringPooling. This makes things up to 20% faster on dalvikvm for some data sets.

gson/src/main/java/com/google/gson/stream/JsonReader.java

@@ -188,6 +188,8 @@ public final class JsonReader implements Closeable {
   /** The only non-execute prefix this parser permits */
   private static final char[] NON_EXECUTE_PREFIX = ")]}'\n".toCharArray();
 
+  private final StringPool stringPool = new StringPool();
+
   /** The input JSON. */
   private final Reader in;
 
@@ -942,7 +944,7 @@ public final class JsonReader implements Closeable {
           if (skipping) {
             return "skipped!";
           } else if (builder == null) {
-            return new String(buffer, start, pos - start - 1);
+            return stringPool.get(buffer, start, pos - start - 1);
           } else {
             builder.append(buffer, start, pos - start - 1);
             return builder.toString();
@@ -1002,7 +1004,7 @@ public final class JsonReader implements Closeable {
           if (skipping) {
             return "skipped!";
           } else if (builder == null) {
-            return new String(buffer, start, pos - start);
+            return stringPool.get(buffer, start, pos - start);
           } else {
             builder.append(buffer, start, pos - start);
             return builder.toString();
@@ -1043,7 +1045,7 @@ public final class JsonReader implements Closeable {
       if (pos + 4 > limit && !fillBuffer(4)) {
         throw syntaxError("Unterminated escape sequence");
       }
-      String hex = new String(buffer, pos, 4);
+      String hex = stringPool.get(buffer, pos, 4);
       pos += 4;
       return (char) Integer.parseInt(hex, 16);
 

gson/src/main/java/com/google/gson/stream/StringPool.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2011 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gson.stream;
+
+/**
+ * A pool of string instances. Unlike the {@link String#intern() VM's
+ * interned strings}, this pool provides no guarantee of reference equality.
+ * It is intended only to save allocations. This class is not thread safe.
+ */
+final class StringPool {
+
+  private final String[] pool = new String[512];
+
+  /**
+   * Returns a string equal to {@code new String(array, start, length)}.
+   */
+  public String get(char[] array, int start, int length) {
+    // Compute an arbitrary hash of the content
+    int hashCode = 0;
+    for (int i = start; i < start + length; i++) {
+      hashCode = (hashCode * 31) + array[i];
+    }
+
+    // Pick a bucket using Doug Lea's supplemental secondaryHash function (from HashMap)
+    hashCode ^= (hashCode >>> 20) ^ (hashCode >>> 12);
+    hashCode ^= (hashCode >>> 7) ^ (hashCode >>> 4);
+    int index = hashCode & (pool.length - 1);
+
+    String pooled = pool[index];
+    if (pooled == null || pooled.length() != length) {
+      String result = new String(array, start, length);
+      pool[index] = result;
+      return result;
+    }
+
+    for (int i = 0; i < length; i++) {
+      if (pooled.charAt(i) != array[start + i]) {
+        String result = new String(array, start, length);
+        pool[index] = result;
+        return result;
+      }
+    }
+
+    return pooled;
+  }
+}