Order what happens when an object is created and then used.

1. Memory is set aside to hold the new object's fields
2. The constructor runs, with the arguments given at the point of creation
3. The constructor rejects or corrects any argument that would break the invariant
4. The object is handed back to the caller with its class invariant holding
5. A public method is called, and may assume the invariant holds on entry

Allocation comes first because the constructor needs fields to write into. The constructor then validates before the object escapes: that ordering is the whole point, since an object handed back in a broken state can never be repaired by the methods, which were written assuming the invariant already holds. Letting the object reach the caller before validation is the error, by then any method may already have been called on it.