Running Groovy command from Jenkins using Groovy script plugin

Question

I want to force following scenario in Jenkins:

1. I have job A and job B
2. I want to disable job A when job B is executed, and after execution of job B, I

Answer 1

I ran into the same problem "unable to resolve class jenkins.model.Jenkins" as commented by @iloveretards, until I realized I had tried to use the build step "Execute Groovy script". After switching to build step "Execute system Groovy script", this actually worked as intended:

import jenkins.model.Jenkins
Jenkins.instance.getItem("job-name").disable()