Modified the model (#2)

* Modified the model

* Added more tests and fixed some comments

Author: yaozhaoy

.gitignore

@@ -8,5 +8,6 @@ build
 .project
 .idea
 *.iml
+out
 .settings
 

build.gradle

@@ -1,11 +1,18 @@
 /*
- * This file was generated by the Gradle 'init' task.
+ * Copyright 2020 Amazon.com, Inc. or its affiliates.
+ * 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.
  *
- * This generated file contains a sample Java Library project to get you started.
- * For more details take a look at the Java Libraries chapter in the Gradle
- * User Manual available at https://docs.gradle.org/6.5.1/userguide/java_library_plugin.html
  */
 
+
 plugins {
     // Apply the java-library plugin to add support for Java Library
     id 'java-library'