installing a downloaded R source package file

From within R :

If the destdir argument is used, the downloaded packages are not deleted after the installation (or if the compilation fails) :
> install.packages("rJava", dep = T, destdir = "/home/user/Downloads/") :

If the compilation fails, one can get back later on the process by specifying the source file on disk :
> install.packages("/home/user/Downloads/rJava_0.8-4.tar.gz", repos=NULL)