A 30-Day Software Engineer Interview Preparation Plan (Java, DSA and System Design)
By Preeti Verma
Thirty days is enough to prepare well for a software engineering interview if you use it deliberately. This plan assumes you already work as a developer and can give roughly one and a half to two hours on weekdays and three to four on weekends. Adjust the pace to your schedule, but keep the order.
The principle
Do a little of everything every week, rather than finishing one topic before starting the next. Interview skills fade quickly without repetition, and mixing topics is closer to the real interview.
Week 1: fundamentals and a baseline
Goal: know where you stand.
- Day 1: take a 30-minute mock interview and read the feedback. This is your baseline. You will repeat it in week 4.
- Days 2 to 4: language fundamentals. For Java: collections (especially HashMap), equals and hashCode, immutability, exceptions. Answer questions out loud.
- Days 5 to 6: two DSA patterns, for example arrays with two pointers and hash maps. Two or three problems per pattern.
- Day 7: rest, or a light review of what you wrote down.
Week 2: depth and patterns
Goal: get comfortable with the harder questions.
- Concurrency: race conditions, synchronized versus volatile versus atomics, thread pools and CompletableFuture. See our Core Java guide.
- Framework and database: for backend roles, Spring Boot internals and SQL (joins, indexing, second-highest salary). Our Spring Boot scenarios cover the common ones.
- DSA: sliding window and binary search, then stacks and queues.
- End of week: a 15-minute mock on a topic you feel weakest in.
Week 3: design and systems
Goal: be able to talk through a design calmly.
- Days 15 to 17: high-level design basics using the framework in our system design guide. Design a URL shortener end to end.
- Days 18 to 19: low-level design. Do an LRU cache and a parking lot.
- Days 20 to 21: DSA: trees, graphs and dynamic programming basics (coin change, longest increasing subsequence).
- Keep the daily spoken answer going.
Week 4: simulate and sharpen
Goal: turn knowledge into performance.
- Day 22: repeat the 30-minute mock from day 1 and compare feedback. Notice what improved.
- Days 23 to 25: company-specific preparation. If you know the company, study the questions candidates report for it. See our guides to JP Morgan and Goldman Sachs.
- Days 26 to 27: prepare your stories: a project deep dive, a conflict, a failure and a proud result. Practise Tell me about yourself and Why are you leaving?.
- Days 28 to 29: full mocks, timed, with no notes.
- Day 30: light review and rest. Sleep matters more than one more problem.
Daily routine (about 90 minutes)
- 20 minutes: revise yesterday's weak spots.
- 40 minutes: the day's main topic.
- 20 minutes: speak two answers aloud, with a timer.
- 10 minutes: write down what you got wrong.
How to track progress
Keep a simple list of questions you could not answer, and remove them when you can. Check the list every Sunday. If a topic keeps reappearing, spend the next week's extra time on it. Progress trackers in the Resources section save your ticked-off questions to your account, so you can see how much of a list you have covered.
What to do if you have less time
With ten days, keep the daily spoken answers, drop the breadth and go deep on the three topics the company asks about most. With three days, do two mocks, revise your project story and sleep.
A word on confidence
Most candidates feel underprepared even when they are ready. Mocks help because they replace a vague feeling with evidence: you can see your feedback improve. Practise the interview before the interview and the real one feels familiar.