hyperledger or ethereum?

Hi All,
I am between jobs and started to invest in cryptos and ICOs and that lead me to decide to switch to a career in blockchain!
I am a backend developer with experience in C, C++, Java, RDBMS and decent exposure to python, perl, javascript, node.js, AWS in wide variety on companies.

I actually started to study Cryptocurrency course from Coursera by Princeton, but their assignments are based in Java.
Why Java when blockchains use C, C++ and smart contracts use scripting languages?

I looked and some job postings and most of them ask for hyperledger or ethereum experience.
Most of the ICOs use ethereum while hyperledger is more for enterprises I believe.
Any thoughts on which is more lucrative and which one has more scope and demand?
And the best way to study these?

Any suggestions where I can contribute to some open source project to gain experience?
Or work for a startup for no salary?

Thanks so much