我在android studio 2.3中尝试了数据绑定，但它给出了错误

Question

我尝试了一个简单的数据绑定示例，但它给出了错误。

当我尝试运行此代码时，它会给出＆＃34;错误：（122,95）错误：无法找到符号变量com＆＃34;

MainActivity.class

public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
 ActivityMainBinding activityMainBinding=DataBindingUtil.setContentView(this,R.layout.activity_main);
    User user=new User("Android","Dev");
    activityMainBinding.setUser(user);    }

}

User.class

public class User {
private String name;
private String lastName;
public User(String name, String lastName) {
    this.name = name;
    this.lastName = lastName;
}

public String getName() {
    return name;
}

public String getLastName() {
    return lastName;
}
}

activity_main.xml

 <?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="root.com.myapplicationbinding.MainActivity">
    <data>
    <variable
        name="user"
        type="root.com.myapplicationbinding.User" />
</data>
<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
   >

<TextView
    android:id="@+id/firstnameLabel"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@{user.name}" />

<TextView
    android:id="@+id/firstnameTextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@{user.lastName}"
    android:layout_toRightOf="@+id/firstnameLabel"/>
</RelativeLayout>

</layout>