When you go into command prompt or a terminal window, you get a prompt at the left showing where you are.
On Windows you tend to start in MyDocuments or similar. Which folder did you put the MyFirstApp file in? Maybe it was c:\\java\apps, in whihc case write "cd c:\\java\apps" and go to that folder. Then try "dir" (Windows) or "ls" (*nix) to find the contents of that folder. Then try again.
If you are on Windows and have the app on a floppy disc, try simply writing "a:" to get to the floppy disc.
As I said, try something different from Notepad. It is notorious for appending .txt to the name of your files. To see those extensions go into
Un-tick/un-check "hide extension for known file types."
If you still use Notepad, you have to put "" quotes round the name of the file when you use save as
Then you can see how many files you have called MyFile.java and how many called MyClass.java.txt.
Try Notepad++; when you save the file with a .java extension, it gives automatic indentation, highlights matching bracket pairs, and displays keywords in different colours. Makes programming much easier. The other app I recommended, Notepad2, is also better than Notepad.
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