Why does the extension not change to .tar using tools.tar api?

hi...i used the org.apache.tools.tar api for tarring the files...The issue is the resultant file's extension is not ".tar"..ideally it shud be ".tar"..isnt it?...because the unix command "tar -cvf tar_file file1 file2"....gives the output as tar_file.tar....

And the size of tar file using this api is > than the one made by Unix command "tar"...

Can anybdy plz suggest, how to overcome thi sproblem?

[423 byte] By [javaFanMana] at [2007-11-27 4:38:21]