Threads - Pointing out the correct statements Questions and Answers

Answer: C

Its worker threads are non-daemon by default and stay alive waiting for more work, so a program that never calls shutdown does not exit even after all its tasks are done. Forgetting the call is a common reason a JVM appears to hang at the end of a run.

Answer: D

The JVM creates a thread to run main, so single-threaded code is really one-thread code. That thread is not a daemon, which is why the program does not exit while it is still running, and it is the thread whose name Thread.currentThread().getName() reports as main.

Answer: A

Scheduling is left to the platform, so nothing about relative order is promised and a program that happens to print in a tidy order on one run may not on the next. Any required ordering has to be imposed explicitly, with join, a lock, a latch or a queue.

Answer: B

A finished thread is TERMINATED, and the javadoc states a thread may not be restarted once it has completed execution; a second start() throws IllegalThreadStateException. Reusing the object is impossible, which is one reason executors exist: they reuse threads while you submit fresh tasks.

Answer: C

The keyword marks a method or a block; there is no synchronized class and no synchronized field. Making a field's individual reads and writes atomic and visible is what volatile does, and neither keyword makes a compound update such as an increment safe on its own.

Answer: D

start() takes no arguments and run() declares none, so anything the task needs is supplied when the Runnable or Thread is constructed, or captured by a lambda. Captured locals must be effectively final, which is one reason shared mutable state tends to live in a field instead.

Answer: A

Atomicity of a single write is not the issue: each write lands whole, but without ordering or visibility guarantees one thread can overwrite the other's value or read a stale one, so an update disappears. The write being atomic is exactly why this looks safe and is not.

Answer: B

Every other thread needing the monitor waits for the whole region, so holding it across slow work such as I/O or a sleep serialises the program. The block still has to be long enough to cover the whole invariant, since splitting it lets another thread observe a half-finished update.

Answer: C

Interruption sets a flag and nothing more for a thread that is simply running; a loop that never consults it runs to completion regardless. That cooperative model is deliberate, because stopping a thread at an arbitrary point is what made stop() unsafe.