HashMap.HashMap1 lazily initializes and then caches the key value pair kv. So it keeps redundant information, presumably to avoid creating key value pairs when repeatedly iterating over all elements.

From my experience, short-lived objects are very cheap on the JVM while long-lived objects come with a larger penalty. In addition, keeping redundant information significantly complicates the code and has the potential to become inconsistent, which has already happened in this case.

So it should be investigated if it is really worth it to keep kv around, or if the code could be simplified by either

• removing kv and creating it on demand
• storing just kv and getting key and value from kv when needed