J is a very rich language. You could study and use it for years, and still consider yourself a beginner. This is in sharp contrast to simpler languages like Basic or Java, where months of concerted study and use would make you an expert. The effort required to become an expert J programmer is closer to that required to become an expert C++ programmer.
The good news is that the essence of J is so simple and consistent, that you can quickly learn enough to start solving real and interesting problems.
It is easier to learn enough Basic or Java to solve trivial problems, but it is easier to learn enough J to solve more interesting and challenging problems. And once you have that level of skill under your belt, you are not at the end of the road, but can continue to improve, making yourself a better and more formidable programmer.
J is particularly strong in the mathematical, statistical, and logical analysis of arrays of data. It is a powerful tool in building new and better solutions to old problems and even better at finding solutions where the problem is not already well understood.
As well as being a general purpose programming language, the J system also provides:
an integrated development environment
standard libraries, utilities, and packages
a form designer for your application forms (windows)
an event-driven graphical user interface to your application
several methods of interfacing with other programming languages and applications
rapid application prototyping and development
royalty-free distribution of run-time versions of your application
If you are interested in programming solutions to challenging data processing problems, then the time you invest in learning J will be well spent.