Threads - General Questions Questions and Answers

Answer: C

stop is deprecated, as are suspend and resume, because they leave shared state in an unpredictable condition. join, interrupt and setDaemon are all current API. Compiling a call to a deprecated method still succeeds; the compiler only warns.

Answer: D

stop, suspend and resume are the deprecated trio, together with countStackFrames. join, yield, interrupt, sleep, setPriority and isAlive are all supported. The three were withdrawn together because each can leave locks or state inconsistent.

Answer: A

isAlive answers a yes or no question and returns a boolean. getState returns a Thread.State for finer detail, and neither method takes an argument. Confusing the two usually shows up as trying to compare isAlive against a state constant.

Answer: B

A constructor cannot be declared synchronized, because no other thread can reach the object until construction finishes. Instance methods, static methods and blocks may all carry the keyword. A synchronized block inside a constructor is legal if a lock is genuinely needed.

Answer: C

volatile and final cannot be combined: final says the value never changes after construction, while volatile exists to publish changes, so the pair is contradictory and the compiler rejects it. Every other combination shown is legal.

Answer: D

Thread implements Runnable, so a Thread reference is assignable to a Runnable variable. Runnable is an interface and cannot be instantiated directly without a body, and an Object is not a Thread so the last assignment needs a cast that would fail at runtime anyway.

Answer: A

Correct answer: One

Runnable declares only run(), which is what makes it a functional interface and so expressible as a lambda. Having exactly one abstract method is the requirement for that, and it is why Runnable, Callable and Comparator can all be written as lambdas.

Answer: B

There is no SLEEPING state. A sleeping thread is reported as TIMED_WAITING, the same state as one in wait with a timeout or join with a timeout. The enum names describe why a thread is not running rather than which method put it there.

Answer: C

sleep takes milliseconds as a long, with a second form adding nanoseconds as an int. There is no overload taking a TimeUnit; that style belongs to the java.util.concurrent classes. An int argument widens to long automatically, which is why sleep(500) compiles.

Answer: D

setDaemon is an instance method taking a boolean. Java has no conversion from int to boolean, the flag is not an accessible field, and there is no static two-argument form. The call must also come before the thread is started.