As I wrote in my previous blog post, I'm glad to see strong values of technical excellence, helping others and contribution in the OpenJDK community.
Software architect and lambda guru Brian Goetz brought my attention to an example of someone doing valuable contributions to Java. A Japanese student under the nickname "bitter_fox" did a series of patch suggestions on the OpenJDK email list "lambda-dev". You can see the suggestions he made, e.g. in the July mail archive for lambda-dev.
Bitter_fox found problems, investigated and then presented the background and patch suggestions on the email list. Really valuable for the progress of a project. Brian Goetz ended up sending him a symbolic token of appreciation with a small packet of Java souvenirs, I don't read Japanese, but you can see the google translate of his unboxing blog post.
There are around 100 mailing lists, join a couple of them out of interest for the area and see what's going on, maybe you can find a way to contribute to Java.