whether the Android FragmentTransaction.replace() is thread safety?

Question

I remember only the UI Thread can modify the View of the Activity, no-UI Thread can not modify the view. So whether the method "replace()" which you will find in the code is thread safety ? if the code is right, why that method can do that ?(Thanks)

This is code:

public class SelectBookActivity extends Activity implements
        BookListFragment.Callbacks
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        // inflate a ListFragment and a container
        setContentView(R.layout.activity_book_twopane);
    }

    // the method in the interface
    @Override 
    public void onItemSelected(Integer id)
    {

        Bundle arguments = new Bundle();
        arguments.putInt(BookDetailFragment.ITEM_ID, id);

        BookDetailFragment fragment = new BookDetailFragment();

        fragment.setArguments(arguments);

        getFragmentManager().beginTransaction()
            .*replace*(R.id.book_detail_container, fragment)
            .commit();  
    }
}

Answer 1

the method commit() Schedules a commit of this transaction. The commit does not happen immediately; it will be scheduled as work on the main thread to be done the next time that thread is ready.