Java Programming

I m having a problem when i import the following library...
import java.io.File;


netbeans underlines "File" and gives error "cannot find symbol"

i tried
import java.io.*;

but that doesn't allow:
File myFile= new File("fileName.txt");

here netbeans underlines "fileName.txt" and again gives error "cannot find symbol"

please tell me how to fix it...
In fact i m writing a code to rename a file.... i got a number of coeds from net but for every one either "import java.io.*;" or "import java.io.File;" is needed. If you have any other idea to "Rename a file" please share with me....
thx a lot