You should use the secondary constructor for File to specify the directory in which it is to be symbolically created. This is important because the answers that say to create a file by prepending the directory name to original name, are not as system independent as this method.
Sample code:
String dirName = /* something to pull specified dir from input */;
String fileName = "test.txt";
File dir = new File (dirName);
File actualFile = new File (dir, fileName);
/* rest is the same */
Hope it helps.