Increase default JSON string buffer capacity

gson/src/main/java/com/google/gson/Gson.java

@@ -588,7 +588,7 @@ public String toJson(Object src) {
    * @see #toJson(Object)
    */
   public String toJson(Object src, Type typeOfSrc) {
-    StringBuilder writer = new StringBuilder();
+    StringBuilder writer = JsonElement.newJsonStringBuilder();
     toJson(src, typeOfSrc, writer);
     return writer.toString();
   }
@@ -706,7 +706,7 @@ public void toJson(Object src, Type typeOfSrc, JsonWriter writer) throws JsonIOE
    * @since 1.4
    */
   public String toJson(JsonElement jsonElement) {
-    StringBuilder writer = new StringBuilder();
+    StringBuilder writer = JsonElement.newJsonStringBuilder();
     toJson(jsonElement, writer);
     return writer.toString();
   }

gson/src/main/java/com/google/gson/JsonElement.java

@@ -94,6 +94,9 @@
  * @author Joel Leitch
  */
 public abstract class JsonElement {
+
+  private static final int DEFAULT_JSON_BUFFER_SIZE = 256;
+
   /**
    * @deprecated Creating custom {@code JsonElement} subclasses is highly discouraged and can lead
    *     to undefined behavior.<br>
@@ -420,7 +423,7 @@ public short getAsShort() {
   @Override
   public String toString() {
     try {
-      StringBuilder stringBuilder = new StringBuilder();
+      StringBuilder stringBuilder = newJsonStringBuilder();
       JsonWriter jsonWriter = new JsonWriter(Streams.writerForAppendable(stringBuilder));
       // Make writer lenient because toString() must not fail, even if for example JsonPrimitive
       // contains NaN
@@ -431,4 +434,8 @@ public String toString() {
       throw new AssertionError(e);
     }
   }
+
+  static StringBuilder newJsonStringBuilder() {
+    return new StringBuilder(DEFAULT_JSON_BUFFER_SIZE);
+  }
 }

gson/src/main/java/com/google/gson/TypeAdapter.java

@@ -158,7 +158,7 @@ public final void toJson(Writer out, T value) throws IOException {
    * @since 2.2
    */
   public final String toJson(T value) {
-    StringBuilder stringBuilder = new StringBuilder();
+    StringBuilder stringBuilder = JsonElement.newJsonStringBuilder();
     try {
       toJson(Streams.writerForAppendable(stringBuilder), value);
     } catch (IOException e) {

gson/src/test/java/com/google/gson/GsonTest.java

@@ -60,6 +60,11 @@ private static Gson createGson() {
     return gsonBuilder.create();
   }
 
+  @Test
+  public void testDefaultJsonStringBuilderCapacity() {
+    assertThat(JsonElement.newJsonStringBuilder().capacity()).isEqualTo(256);
+  }
+
   @Test
   public void testStrictnessDefault() {
     assertThat(new Gson().strictness).isNull();