The job duties of a part-time Java developer focus on designing, testing, and debugging software and applications using the Java computer language. As a part-time professional, you work less than 40 hours per week. Since Java is a popular application coding language, your responsibilities often involve working on app development projects. A developer can also look for ways to update or improve existing applications. Some employers or clients may ask you to write code for customized applications that they can use on their network or computer system. Java coders can also work on mobile apps for the Android platform.