In Java, there are 4 platforms or editions.
1. Java Standard Edition (Java SE)
It is a standard java programming platform which includes many Java APIs like java.lang, java.io, java.util, java.math etc.
It mainly includes Java core topics like OOPs, String, Regex, Exception Handling, Inner classes, Multithreading, Networking, AWT, Swing, Collection etc.
2. Java Enterprise Edition (Java EE)
It is an enterprise java programming platform which is used to create web as well as enterprise applications.
It includes Java topics like Servlet, JSP, Web Services, EJB etc.
3. Java Micro Edition (Java ME)
It is a micro java programming platform which is used to develop mobile applications.
It is a java programming platform which uses light weight user interface API and used to develop rich internet applications.