The ZipOutputStream class is used to write ZIP files to a file or other stream. A ZIP file consists of a number of entries. Usually each entry corresponds to a file in the directory structure being zipped. There is a method on ZipOutputStream that is slightly confusingly named putNextEntry. Despite its name, it does not write a whole entry. Instead, it writes the metadata for an entry. The content for that entry is then written using the write method. Finally the entry is closed using closeEntry.

Therefore, if you call putNextEntry and closeEntry but omit the call to write, an empty ZIP file entry is written to the output stream.