public K getKey() {
      return key;
    }
Key-value entry. This class is never exported out as a user-mutable Map.Entry (i.e., one
supporting setValue; see MapEntry below), but can be used for read-only traversals used in bulk
tasks. Subclasses of Node with a negative hash field are special, and contain null keys and
values (but are never exported). Otherwise, keys and vals are never null.
geode-core/src/main/java/org/apache/geode/internal/concurrent/CompactConcurrentHashSet2.java