Java Interview Questions in Kolkata

Use a dedicated executor for I/O work. ExecutorService pool = Executors.newFixedThreadPool(4); CompletableFuture<User> user = CompletableFuture.supplyAsync(() -> userApi.get(id), pool); CompletableFuture<List<Order>> orders = CompletableFuture.supplyAsync(() -> orderApi.list(id), pool); Profile p = user.thenCombine(orders, Profile::new) .orTimeout(2, TimeUnit.SECONDS) .join();

The switch needs no default because the type set is closed. sealed interface Shape permits Circle, Rect {} record Circle(double r) implements Shape {} record Rect(double w, double h) implements Shape {} static double area(Shape s) { return switch (s) { case Circle c -> Math.PI * c.r() * c.r(); case Rect(double w, double h) -> w * h; }; }

Use a record with @ConfigurationProperties. @ConfigurationProperties(prefix = "payment") @Validated public record PaymentProps( @NotBlank String baseUrl, @Min(100) int timeoutMs) {} // application.yml // payment: // base-url: https://pay.internal // timeout-ms: 2000 Enable it with @ConfigurationPropertiesScan on the main class. The app fails at startup if values are invalid.

A token bucket with synchronized refill is simple and correct. class RateLimiter { private final long capacity, refillPerSec; private double tokens; private long last = System.nanoTime(); RateLimiter(long cap, long rps) { capacity = cap; refillPerSec = rps; tokens = cap; } synchronized boolean tryAcquire() { long now = System.nanoTime(); tokens = Math.min(capacity, tokens + (now - last) / 1e9 * refillPerSec); last = now; if (tokens >= 1) { tokens--; return true; } return false; } } Across servers, keep the bucket in Redis.