Object-Oriented & Data-Structure Design

Atlassian runs its live coding as two sittings. One is a straight data-structures round; the other, the one candidates tend to remember, is called Code Design. In Code Design you are handed a real-world prompt with the method signatures already stubbed out. You fill them in with code that compiles, runs, and passes the interviewer's tests inside the hour. Then they start pulling on it: make this faster, make it handle a new case, defend why you stored it that way. It is low-level design that gets executed, not sketched on a whiteboard.

The data-structures sitting leans on the same muscle. Engineers who interviewed describe being asked to implement a structure to spec, often with a little object modeling folded in, a class with a custom comparator rather than one lonely function. The problems here are the ones that recur most in that design bucket: a rate limiter, a cache, and a versioned key-value store, each running behind Jira and Confluence. The lesson closes on the cloud a Premium question, the Code Design prompt candidates report most by name, which turns a billing timeline into a sweep-line problem. All four reward the same habit. State the model and the complexity aloud before you type, then write something clean enough that the follow-up is an extension and not a rewrite.

The Atlassian angle

Treat Code Design as pair-programming against a clock, because a working, tested solution is the grade and an elegant half-finished one is not. Atlassian says plainly that it cares how you think over how fast you type, and that a missing line will not sink you. True, but it's also a trap. At senior levels, two things quietly sink an otherwise strong coder: needing hints to reach something that runs, and not finishing. So narrate continuously, settle the signatures and the edge cases with the interviewer before you code, and drive all the way to green tests. What they want to watch is you modeling a domain and then evolving it, which is the daily work of shipping a feature into a codebase millions of teams depend on.