Pluralsight, the best bang for your buck
After looking at multiple online resources to learn new programming languages and get a refresher on ones you already have experience pluralsight.com is by far the best website to use. It has different paths based on different frameworks and practice tests to show your improvement over time. Some of the paths that I have has used are: Angular, Core Spring, and Java. You can get a 10 day free trial by clicking the link here . I highly recommend that you have an idea of what programming language you want to learn/improve on before getting the trial and get the most out of it.