A map entry (key-value pair). The Map.entrySet method returns a collection-view of the map, whose elements are of this class. The only way to obtain a reference to a map entry is from the iterator of this collection-view. These Map.Entry objects are valid only for the duration of the iteration. More formally, the behavior of a map entry is undefined if the backing map has been modified after the entry was returned by the iterator, except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator.