我认为CollinD的答案是适当的：

All of Guava’s methods for transforming and filtering produce lazy
results… the function/predicate is only applied when needed as the
object is used. They don’t create copies. Because of that,though,a
transformation can easily break the requirements of a Set@H_404_11@.

Let’s say,for example,you have a Map<String,String>@H_404_11@ that contains
both “1” and “01” as keys. They are both distinct String@H_404_11@s,and so the
Map@H_404_11@ can legally contain both as keys. If you transform them using
Long.valueOf(String)@H_404_11@,they both map to the value 1@H_404_11@. They are
no longer distinct keys. This isn’t going to break anything if you
create a copy of the map and add the entries,because any duplicate
keys will overwrite the prevIoUs entry for that key. A lazily
transformed Map@H_404_11@,would have no way of enforcing unique keys
and would therefore break the contract of a Map@H_404_11@.