Java doesn't have Object or any Object derivative arrays. Only elementary types can be arrays. Of which reference type is one. So when you say: Integer[] box

Java doesn't have Object or any Object derivative arrays. Only elementary types can be arrays. Of which reference type is one. So when you say: Integer[] boxedInts = new Integer[5]; You're allocating an array of references with length of 5, so usually 5 * 4 + 8 bytes. Additionally, each of the referenced Integer Object instance take up 16 bytes. Multiple arrays (or reference fields) can refer to same Object instance. The example was about Integers, but it's basically the same story for FactoryWorkerPersons. Java doesn't have arrays of objects. Only arrays of elementary types, up to 2^31-1 entries.