Technical interview questions and drills

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How can a Java application have a memory leak despite garbage collection?

Defines managed memory leaks as unwanted reachability and connects caches, listeners, class loaders, ThreadLocal values, and queues to retaining paths.

Java

Concept questionHard~10 min

Drills

How can a Java application have a memory leak despite garbage collection?

How do atomic variables and compare-and-set work in Java?

How does Java garbage collection decide which objects can be reclaimed?

How do Java deadlocks happen, and how do you prevent them?

How do virtual threads differ from platform threads in Java?

How do you design an ExecutorService for a Java backend?

How do you reason about garbage-collection latency, throughput, and tuning?

How do you use Java thread dumps to diagnose a slow or stuck service?

How should interruption and cancellation work in Java?

How would you diagnose OutOfMemoryError in a Java service?

How would you diagnose thread-pool starvation in a Java service?

What causes a race condition, and how do you make Java code thread-safe?

What does happens-before mean in the Java Memory Model?

What guarantees does synchronized provide in Java?

What is safe publication in Java, and how does immutability help?

What is the difference between allocation pressure and memory retention in Java?

What is the difference between concurrency and parallelism in Java?

What is the difference between Future and CompletableFuture in Java?

What JVM memory areas matter to a Java backend service?

When do you use volatile, synchronized, or atomic variables in Java?

When is ThreadLocal useful, and what lifecycle risks does it create?

When should you use ConcurrentHashMap or another concurrent collection?

When should you use wait and notify instead of higher-level Java concurrency tools?

When would you choose ReentrantLock instead of synchronized?