private void onCollectionClicked(Long collectionId){
  Intent intent=new Intent(this,ProductListActivity.class);
  if (collectionId != null) {
    intent.putExtra(ProductListActivity.EXTRA_COLLECTION_ID,collectionId);
  }
  startActivity(intent);
}

private void onCollectionClicked ( Long collectionId ) { Intent intent = new Intent ( this , ProductListActivity . class ) ; if ( collectionId != null ) { intent . putExtra ( ProductListActivity . EXTRA_COLLECTION_ID , collectionId ) ; } startActivity ( intent ) ; }
when the user picks a collection , launch the product list activity to display the products in that collection .
