$ curl -C - https://download.java.net/java/ga/jdk11/openjdk-11_osx-x64_bin.tar.gz -O openjdk-11_osx-x64_bin.tar.gz
$ tar xf openjdk-11_osx-x64_bin.tar.gz
$ sudo mv jdk-11.jdk /Library/Java/JavaVirtualMachines/
$ java -version
openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)