Good onBackPressed() behavior closing the navigation drawer when it is open and going back when it is not.

onBackPressed.java

@Override
public void onBackPressed() {
  DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
  if (drawer.isDrawerOpen(GravityCompat.START)) { 
    // If the drawer is open close the drawer
    drawer.closeDrawer(GravityCompat.START);
  } else {
    // Otherwise do the back pressed operation
    super.onBackPressed();
  }
}