Before all the FUD comments appear:

- OpenJDK is the reference implementation, it has the same license as the linux kernel, and almost all of the “alternative” JDKs you might have used are all repackaged OpenJDKs with minimal patches. OracleJDK is also like that.

- Java is completely free and libre. You can choose to pay for it the same way you can seek out Red Hat for a paid support license. The kernel/OpenJDK itself is completely open-source.

- OracleJDK itself has a “freemium” model, where you can use the latest LTS release freely, until the next one comes along (plus one year).

- Open JDK is being developed like 90+% by developers employed by Oracle