In this paper a marking system for Java programming is presented which has been developed as a plug-in for a widely used editor, Eclipse. This system runs student submitted programs against previously defined test cases. Depending on the percentage of correct running code, a proper mark is awarded. Since this program was implemented in order to be used in a principles of programming course, we require students to practice coding with a correct style. Therefore, this system checks the style of the code and produces messages when a better style is expected. In some cases penalty marks are considered for improper code style. For this system to play an educational role, we allow students to submit more than once. With this we aim to help them learn from their mistakes. The number of submissions differs from one exercise to another and is defined dynamically by our system administration.We call this system JavaMarker.