How to change the JDK for a Jenkins job?

Question

I have imported the jenkins jobs from existing jenkins server from another machine. But

Answer 1

Here is my experience with Jenkins version 1.636: as long as I have only one "Install automatically" JDK configured in Jenkins JDK section, I don't see "JDK" dropdown in Job=>Configure section, but as soon as I added second JDK in Jenkins config, JDK dropdown appeared in Job=>Configure section with 3 options [(System), JDK1, JDK2]