All things Java will appear in this book, over time....
If you need some help just Getting Java then clearly head there.
Personally I think A guide to Java versions and features is a good introduction to Java versions and releases etc, so do take 10 minutes out to read it. Then take a look at Dev.java: The Destination for Java Developers which is a great place to start learning.
It is important to note that the NPAPI is being phased out and so Java Applets will cease to work. See NPAPI Plugin Perspectives and the Oracle JRE (Java Platform Group, Product Management blog) for more details.
The future is in Java Web Start, where a Java app is launched, see Java Web Start in or out of the browser (Java Platform Group, Product Management blog) which provides a good starting point for learning about Java Network Launching Protocol (JNLP).
If you need source code for an Open Source library then CodeNav is a very handy site.
There is Java Enterprise Edition on GitHub, see Java EE.
I have got a Geoff Does Stuff code repository on GitLab and GitHub with Java examples, built using Gradle, this should be easier to use than general code snippets.
As with my main repository, the code is committed to GitLab and mirrored in GitHub.
There are some useful, official websites and YouTube content that are well worth examining.