Link to abstractcrushingrecipe
Importing the class
Link to importing-the-class
It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.
Link to extending-processingrecipe
AbstractCrushingRecipe extends ProcessingRecipe. That means all methods available in ProcessingRecipe are also available in AbstractCrushingRecipe