This class represents a sparse entry in a Tar archive.

The C structure for a sparse entry is:

struct posix_header {
struct sparse sp[21]; // TarConstants.SPARSELEN_GNU_SPARSE     - offset 0
char isextended;      // TarConstants.ISEXTENDEDLEN_GNU_SPARSE - offset 504
};

Whereas, "struct sparse" is:

struct sparse {
char offset[12];   // offset 0
char numbytes[12]; // offset 12
};

Each such struct describes a block of data that has actually been written to the archive. The offset describes where in the extracted file the data is supposed to start and the numbytes provides the length of the block. When extracting the entry the gaps between the sparse structs are equivalent to areas filled with zero bytes.