The Samples for Java open source project, GitHub.com/BlackBerry/Samples-for-Java, contains the source code for samples previously released through the BlackBerry Developer Knowledge Base. These samples include workarounds, tools, and libraries that extend the BlackBerry Java SDK. Of particular note is the Advanced UI library that includes many advanced buttons, fields and managers. There is also a Titlebar API that backports the BlackBerry OS6 Titlebar API to 4.2.1 through 5.0.
Read more about the components and the repository in this Introduction Post.