If you're writing a Java program using Windows Text Document, the simple notepad program, you'll notice that when you save the file it defaults to a .txt file naturally. In order for Command Prompt to properly read and compile the program, the file extensions must be changed to a .java. We can do this by highlighting the .txt at the end of the file name and replacing it with .java, but you may notice a problem. The file type will still remain a Text Document even though you see it says .java. All that happens is .java gets added to the extension, even though you don't see it. For example, if you're file was Java1.txt it would now be Java1.txt.java or Java1.txt.txt or Java1.java.txt and these will not work. We want the file to be Java1.java. How we do this is very simple, follow the steps below: