This Java class provides an extended JTextField that only allows the user to type in valid double numbers. Additionally, it can be specified if the user may input negative values. This class is part of a project that we had to do in our informatics course in school. You can do with this class whatever you want as long as you keep my name in the upper JavaDoc comment. If you like to, fell free to fork this project and add features. The code is available at GitHub as it is open-source. You can find it here. If you like this small project or if you have suggestions concerning this Java class, just leave them in the comments below.