title: How to fix 'cannot find symbol class Nullable' error in android studio 3
body: <p>i'm using android studio 3.2 , and want to use SQLiteOpenHelper in my blank class . when i have run project java compiler return error : cannot find symbol class Nullable</p>
  
  <pre><code>public class Db extends SQLiteOpenHelper {
  public Db(@androidx.annotation.Nullable Context context, @androidx.annotation.Nullable String name, @androidx.annotation.Nullable SQLiteDatabase.CursorFactory factory, int version) {
      super(context, name, factory, version);
  }}
  </code></pre>
  
  <p>I also used this implementation </p>
  
  <pre><code>implementation 'com.android.support:support-annotations:24.2.0'
  </code></pre>
  
  <p>I clicked Invalidate caches and restart on file menu and rebuild project but error still occurs</p>
  
  <p>Thank you in advance</p>