Unable to find lessons about Interfaces in Java

Greetings Codecademy moderators and members!

I am currently on the ‘CreateREST APIs with Spring and Java’ Skill Path. This week I’ve been looking into two broad lesson modules namely ‘Responding to Requests’ & ‘Spring Context’. The contents of the lessons seem to require a good working understanding of Interfaces, which I do not seem to recall having studied in the previous sections of this particular skill path. I’m unable to locate the ‘Interfaces’ topic anywhere in any of the Java courses. Can someone please point me in the right direction - which course should I refer to gain a deeper understanding about Interfaces in Java