Java Programming

Hi All,
Im using the following piece of code to get the list of files from a directory using FtpClient

try
             {
	String folder="/prod/inx/logs/fe";
	ftp.changeWorkingDirectory(folder);

	files = ftp.listFiles();
	List filesDirs = Arrays.asList(files);
	if(!(filesDirs.isEmpty()))
	{
	System.out.println("Working dir :"+ftp.printWorkingDirectory());
	}
                } 

I have already created the ftp object . My problem is , the function changeWorkingDirectory() is not working. when i try to print the workingdirectory its printing "null". Please help