AtomicInteger updates without a lock

Atomic classes use compare-and-swap, so counters stay correct under contention without synchronized blocks.

Code

var counter = new AtomicInteger();
var pool = Executors.newFixedThreadPool(8);

for (int i = 0; i < 1000; i++) pool.submit(counter::incrementAndGet);
pool.shutdown();
pool.awaitTermination(10, TimeUnit.SECONDS);

System.out.println("expected 1000, got " + counter.get());
System.out.println("accumulateAndGet(x10) = " + counter.accumulateAndGet(10, (a, b) -> a * b));

Output

expected 1000, got 1000
accumulateAndGet(x10) = 10000

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Published 2026-07-30