Threads - General Questions Questions and Answers

Answer: A

Runnable is an interface with a single method. Thread, ThreadGroup and ThreadLocal are all classes, which is why a task class implements the first and extends any of the others only when it genuinely needs their behaviour.

Answer: B

ThreadLocal is a generic class instantiated with new, and its type argument is what get and set exchange. There is no factory on Thread, and get is an instance method returning the stored value rather than a constructor.

Answer: C

Lock, ReentrantLock, ReadWriteLock and Condition all sit in java.util.concurrent.locks, a subpackage of the main concurrency package. Importing java.util.concurrent alone does not bring them in, because an import on demand does not reach subpackages.

Answer: D

AtomicInteger is an ordinary class taking an optional initial value, and both the zero-argument and int-argument constructors exist, so two of these compile. The one shown is the clearer of the pair because it states the starting value. Java has no atomic keyword.

Answer: A

There is no synchronizedGet: the class achieves its guarantees with compare-and-swap instructions rather than with monitors, which is the point of the atomic types. incrementAndGet, compareAndSet and getAndAdd are all genuine members.

Answer: B

The concurrency utilities take a numeric amount together with a TimeUnit constant, rather than assuming milliseconds the way the older Thread methods do. The unit is an enum value, not a String, so a typo is caught at compile time.

Answer: C

await declares InterruptedException, so a caller must either catch it or declare it, and the class is named InterruptedException in full. There is no catches clause in Java; handling happens inside the body with try and catch.

Answer: D

Thread's own run does nothing useful unless a Runnable was supplied, so a subclass overrides run to hold the work. start is inherited and should not be overridden, execute belongs to Executor, and call belongs to Callable.

Answer: A

setUncaughtExceptionHandler is an instance method taking a Thread.UncaughtExceptionHandler. The static counterpart is setDefaultUncaughtExceptionHandler, which takes only the handler and applies to every thread without one of its own.

Answer: B

Correct answer: dumpStack

Thread.dumpStack() prints a stack trace of the current thread, so like sleep and yield it concerns whoever is executing and is static. getName, getStackTrace and setUncaughtExceptionHandler all act on a named thread and are instance methods.