The File file : f.listFiles() make a list of files that are stored into the file object f and stored it in another file object.

Here is an Example:

import java.io.*;

class  ListAllFiles{
    public static void main(String[] args) {
        File f=new File("C:/");
for(File file : f.listFiles()){
System.out.println(file.getName());
    }
}
}