How do I set the Navigation View menu by code?

For now I'm setting the menu through xml, this way:

    <android.support.design.widget.NavigationView
    android:id="@+id/navView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:background="@color/colorBackgroud"
    app:headerLayout="@layout/nav_header"
    app:itemIconTint="@color/textColorPrimary"
    app:itemTextColor="@color/textColorPrimary"
    app:menu="@menu/menu_nav">

But before I set the menu to do a check with if, for this I would need to set it by code, for example ... if (if) user was equal to "administrator" open a menu other than "users" ".

Follow my code for now:

NavigationView navigationView = (NavigationView) findViewById(R.id.navView);
navigationView.setNavigationItemSelectedListener(this);

How do I set the navigationview menu by code?