I tried data binding in android studio 2.3 but it was giving error

I have tried a simple example of data binding but its giving an error.

While I am trying to run this code it gives Error: (122, 95): Cannot find symbolic variable com

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>