CommandLine parses the command line for a description of a set of files
and converts it into a list of individual files to process.
CommandLine does nothing by itself. It is library code you
can incorporate into your own Java programs like this:
   CommandLine wantedFiles = new CommandLine( args,
     new AllDirectoriesFilter() /* which directories to include */,
     new ExtensionListFilter( "java" ) /* which file extensions to include */);
    // iterate through all the files in the collection.
    for ( File file : wantedFiles )
        {
        // files appear in random order, as provided by the OS
        System.err.println( file.getCanonicalPath() );
        }// end for
On the command line, you can specify a list of individual files, mixed
with a list of directories.
The Iteration of Files you get have names as you specified them on the
command line.  If you need canonical names, you must use getCanonicalPath
or GetCanonicalFile.
If you use the -s switch in includes all the files in all the recursive
subdirectories. It must precede the directory names it applies to.
If you use the -q switch, it will suppress the counts of how many files it
found in each subdirectory.  It will be passed through to the application
via isQuiet.
if you use the -v switch, that means verbose.  It will be passed through
to the application via isVerbose.
If you have both -q and -v on the command line, the last option prevails.
Commandline does not currently suupport wildcards, negative selections, or
@indirect lists.
Why that apple tree icon?  It represents a tree of various types of files,
from which you pick some.