It means javac could not find the file you specified, Hello.java. Use "dir" to display the files in the current directory and make sure you have Hello.java.A common cause of this problem occurs when you use an editor like Notepad. Notepad tries hard to add .txt to the end of the file name, so even though you specify Hello.java, the file is saved (by Notepad) as Hello.java.txt. Use "" around the file name in Notepad to solve this problem.