Generally divided into three versions, j2me is oriented to embedded development, such as mobile phone programs. Small and medium-sized software in j2se standard edition should adopt c/s structure, which is also the best start to learn java. J2ee is oriented to large enterprise systems and integrates many technologies. Simply put, you can do game software, chat tools, web development and so on.
If you study JAVA, you can do related work, such as Android programming.
Similarly, if you have JAVA development experience, you will learn other languages quickly, so that you can find related jobs.