To initialize or not initialize JPA relationship mappings?

Question

In one to many JPA associations is it considered a best practice to initialize relationships to empty collections? For example.

@Entity
public class Order {          


        

Answer 1

I would also recommend using Guava's immutable collections, e.g.,

import com.google.common.collect.ImmutableList;
// ...
@OneToMany(mappedBy="order")
List lineItems = ImmutableList.of();

This idiom never creates a new empty list, but reuses a single instance representing an empty list (the type does not matter). This is a very common practice of functional programming languages (Scala does this too) and reduces to zero the overhead of having empty objects instead of null values, making any efficiency argument against the idiom moot.