Javahard

`synchronized` vs `ReentrantLock` - when would you choose one?

Answer

`synchronized` is simpler and uses JVM monitors, giving mutual exclusion and a clear happens-before relationship. `ReentrantLock` is more flexible: `tryLock()`, timeouts, fairness options, and multiple `Condition`s—but you must always `unlock()` in `finally`.

Advanced answer

Deep dive

Expanding on the short answer — what usually matters in practice:

Context (tags): concurrency, locks, synchronized, reentrantlock
JVM: memory (heap/stack), GC, and what drives latency.
Contracts: equals/hashCode/toString, mutability and consequences.
Performance: boxing, allocations, collections, inlining.
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.

Examples

A tiny example (an explanation template):

// Example: discuss trade-offs for "`synchronized`-vs-`reentrantlock`---when-would-y"
function explain() {
  // Start from the core idea:
  // `synchronized` is simpler and uses JVM monitors, giving mutual exclusion and a clear happe
}

Common pitfalls

Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).
Ignoring constraints: memory, concurrency, network/disk costs.