Oracle has a poor record for making it easy to install and configure Java, but using Homebrew, the latest OpenJDK (Java 14) can be installed with:
brew cask install java
For the many use cases depending on an older version (commonly Java 8), the AdoptOpenJDK project makes it possible with an extra step.
brew tap adoptopenjdk/openjdk brew cask install adoptopenjdk8
Existing users of Homebrew may encounter
Error: Cask adoptopenjdk8 exists in multiple taps due to prior workarounds with different instructions. This can be solved by fully specifying the location with
brew cask install adoptopenjdk/openjdk/adoptopenjdk8.