TarEntries that are created from the header bytes read from an archive are instantiated with the TarEntry( byte[] ) constructor. These entries will be used when extracting from or listing the contents of an archive. These entries have their header filled in using the header bytes. They also set the File to null, since they reference an archive entry not a file.

TarEntries that are created from Files that are to be written into an archive are instantiated with the TarEntry( File ) constructor. These entries have their header filled in using the File's information. They also keep a reference to the File for convenience when writing entries.

Finally, TarEntries can be constructed from nothing but a name. This allows the programmer to construct the entry by hand, for instance when only an InputStream is available for writing to the archive, and the header information is constructed from other information. In this case the header fields are set to defaults and the File is set to null.

The C structure for a Tar Entry's header is:

 struct header {
 char name[NAMSIZ];
 char mode[8];
 char uid[8];
 char gid[8];
 char size[12];
 char mtime[12];
 char chksum[8];
 char linkflag;
 char linkname[NAMSIZ];
 char magic[8];
 char uname[TUNMLEN];
 char gname[TGNMLEN];
 char devmajor[8];
 char devminor[8];
 } header;