Performance has always been a part of the main focus of Lucene's development team. Because they are adamant about achieving high efficiency and performance, we have all benefitted from this. To ensure that users can properly leverage Lucene's speed and efficiency, there are best practices that we should adhere to so that we don't introduce unnecessary inefficiency. One of the best practices is to reuse both the Document and field objects. This minimizes the object creation cost during any massive data import operations. It will also reduce the chance of triggering garbage collection.
There are a couple things to keep in mind when reusing Document object: we need to make sure that we clear out all the fields before putting in the new values; for the field, we can just simply overwrite the value.