Java is an evergreen technology platform, and there are lots of top companies who are actively using this platform to solve and address their day to day business challenges. Using the JAVA platform means, using its different related components too. Also you may go to different job sites, and search Java Programmer’s or Java Developer’s jobs; and you will find that the job requirement consists of all different components of Java or J2EE etc.
You may obviously start your training by learning Core Java and as you gain confidence on basic concepts of Java, you can then plan to learn slowly advanced concepts of Java and J2EE frameworks – Spring, Hibernate or Struts etc. This will not only help you explore the Java technology but also help you achieve your Career goals in IT industry.