Cracking the Senior Java Interview: 10 Hardcore Questions on Concurrency

Master these concurrency concepts to ace your senior Java interview

Ahmet Emre DEMİRŞEN

5 min read

·

Jun 3, 2026

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In this article, we will walk through 10 hardcore concurrency questions that frequently appear in senior Java interviews. These aren’t beginner-level “what is a thread” questions—we’re talking about the kind of problems that separate engineers who’ve read a book from those who’ve shipped production systems under load.

Table of Contents

1. Thread Safety and the Java Memory Model
2. Locks, Synchronization, and Deadlocks
3. Concurrent Collections and Their Internals
4. Executors and Thread Pool Tuning
5. Advanced Topics: CompletableFuture, ForkJoinPool, and Volatile

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1. Thread Safety and the Java Memory Model

Question: “What happens when two threads read and write the same variable without synchronization?”

Let’s say we have a simple counter:

public class Counter {
    private int count = 0;

    public void increment() {
        count++;
    }

    public int…