I still remember one interview where I was feeling unusually confident. DSA? Done. SQL? Manageable. Basic Java? Smooth. Then the interviewer smiled and asked: "Can you explain the HAS-A relationship in OOP?" And my brain instantly opened 47 Chrome tabs internally. Because in my mind, OOP relationships were basically: Dog is an Animal Car is a Vehicle Manager is an Employee That's it. I knew inheritance. I knew extends . I knew "IS-A" . I thought I was powerful. Then the interviewer continued: "What's the difference between Aggregation and Composition?" At that moment, even the ceiling fan started judging me. 😅 That interview taught me something important: Knowing syntax is not the same as understanding software design. And honestly, class relationships are one of the most underrated parts of OOP. Most beginners learn classes, objects, constructors, and inheritance — but skip the actual relationships between objects .…