Adyen Coding Interview Questions: Java, Payments and Practical Coding

Adyen, headquartered in Amsterdam, runs a single payments platform that large merchants use to accept payments online, in apps and in stores around the world. Its engineering interviews are among the most language-specific in Europe: most back-end roles are advertised as Java roles, and candidates report questions about Java itself as well as coding and design. This page covers what Adyen builds and who it hires, the process candidates commonly report, the technical depth the teams care about, representative problem types, what interviewers score, and a three-week prep plan.

What Adyen builds and who it hires

Adyen has written that it runs its business on one platform in a single repository, written almost exclusively in Java and split into fairly independent parts along business domains. It manages its own infrastructure in data centres around the world rather than relying entirely on public cloud, and its engineers have written about running very large PostgreSQL databases, used with MyBatis for hand-written SQL. Job posts list Java, RESTful web services, PostgreSQL, Tomcat, Gradle and Elasticsearch, with CockroachDB also mentioned.

• Java software engineers: payment processing, risk, reporting and the merchant platform.
• Front-end engineers: merchant dashboards and checkout components.
• Mobile and point-of-sale engineers: in-person payments and terminals.
• Infrastructure and database engineers: the data centres, PostgreSQL and platform reliability.

What the process tends to look like

Processes differ by team, level and office and change over time, so treat this as the common shape candidates report and confirm the specifics with your recruiter.

Java depth and long-lived code

Java fundamentals. Candidates report questions on collections and their complexity, equals and hashCode, immutability, exceptions, generics and the memory model. Know what the standard library does under the hood, not only how to call it.

Concurrency. Payment platforms process many requests at once. Expect questions on threads, executors, synchronized blocks versus concurrent collections, and how you would make a shared counter or cache safe.

Code meant to last. One candidate describes being asked about writing code that should still be maintainable in ten years, for example Java streams against a plain for-each loop. Adyen values simple, readable code over clever code, so be ready to argue for the plainer option.

Performance. Reports note that performance comes up often. Talk about allocation, choosing the right data structure and measuring before you optimize.

Representative problem types

These are the kinds of problems candidates describe, not a leaked question list. Practice the category, not the exact question.

1. Implement a thread-safe cache or counter in Java.
2. Parse and validate a payment message with strict rules.
3. Design a service that routes payments to different acquirers.
4. Choose between two implementations and defend the more maintainable one.
5. Find duplicate payments in a stream of events.
6. Explain how a HashMap works and what happens on collisions.
7. Medium array, string and hash map problems in Java.

What interviewers score

• Working code: a solution that runs, handles edge cases and is readable by the next engineer.
• Practical judgment: the trade-offs you name and the simplest design that meets the requirement.
• Product sense: understanding who the user is and what failure looks like for them.
• Ownership: examples where you shipped, measured and fixed things yourself.

The behavioral side

Technical rounds decide most outcomes, but every Adyen loop also asks about how you work. Prepare a short story for each of these, with a result and what you learned:

• Something you shipped end to end. Cover the user problem, your decisions, what you measured and what you would change.
• A disagreement with a teammate. Show how you made the decision on evidence and kept the relationship.
• Why this company? Connect its product and engineering problems to the work you want to do next.

Structures and sample answers for the common questions are in our software engineer behavioral answers guide.

A three-week prep plan

1. Week 1: practical coding: build small features against an API, parse and transform data, and write tests, in the language you will interview in.
2. Week 2: system design for the company's domain, plus two behavioral stories about shipping and fixing something under pressure.
3. Week 3: timed mixed problems, a mock interview every other day, and research into the product and its engineering blog.

For practice lists, use LeetCode company-tagged questions; compare the European style of Booking.com and Spotify; and for design rounds, read system design building blocks.

Where CoPilot Interview fits

Most of a Adyen loop is spoken: you explain an approach, defend a trade-off and talk through your past work. CoPilot Interview is an AI interview assistant whose free AI mock interview builds technical and behavioral questions from your résumé and the job description, reads them aloud and scores each spoken answer out of ten, so you can rehearse the explanation as well as the code. The free plan gives 15 minutes a day of live help in sessions of up to 15 minutes, with AI mock interviews included. Online assessments and many coding rounds forbid outside help, so practice beforehand and follow your employer's rules on the day.

Disclosure: CoPilot Interview is our product, so weigh what we say about it accordingly.

Frequently asked questions

What programming language should I use in a Adyen interview?

Java for most back-end roles; the job titles often say so. Front-end and mobile roles use their own stacks, but expect Java questions if the role is listed as a Java engineer.

Does Adyen send an online assessment?

Many candidates report a coding assessment, often on Codility, early in the process, with the solution discussed in a later interview. The number of rounds varies widely in reports, so ask your recruiter what yours will include.

How many interview rounds does Adyen have?

Reports vary a lot, from three rounds to six or seven, typically split between technical interviews and culture-fit conversations. Timelines also vary from about a week to two months. Ask your recruiter for the plan, and note that they often share feedback between stages.

How should I prepare for Adyen coding questions?

Practice practical problems under time limits, build small features against an API in your interview language, and prepare one system design in Adyen's domain. Explain every solution out loud, because follow-up questions about trade-offs matter as much as the first answer.

Can I use AI tools in a Adyen interview?

Only if the instructions you receive say so. Online assessments and live coding rounds generally forbid outside help, and some companies now state their AI policy in the invitation. Use AI to practice beforehand, and follow your employer's rules.