2020 AP Exam questions will cover only Units 1 – 7: AP Computer Science A Units 1-7 at a Glance
The AP Program has online lessons available here
2019-2020 AP CSA Course Syllabus
I recommend installing the Eclipse IDE on your home computer. We use the Eclipse IDE for our classroom development environment. Java development using Eclipse requires the JDK to be installed. Instructions are here: http://bit.ly/eclipse_install
See the College Board Computer Science A Student Page for course and assessment information