Java Threads and Concurrency Flashcards

What happens when `Thread.start()` is called more than once on the same Thread object?

Answer: An IllegalThreadStateException is thrown

Once a thread has been started and has terminated, calling `start()` again on the same Thread object throws `IllegalThreadStateException`.

Which interface should be implemented to return a result from a thread's execution?

Answer: Callable

`Callable` is similar to `Runnable` but its `call()` method returns a result of type V and can throw checked exceptions.

What is thread starvation in Java?

Answer: A thread being perpetually denied CPU access due to other higher-priority threads

Thread starvation occurs when a thread cannot gain regular access to shared resources because other threads are always prioritized.

Which keyword modifier ensures a method can only be executed by one thread at a time, locking on the instance?

Answer: synchronized

An instance `synchronized` method acquires the monitor lock of `this` object, preventing concurrent execution by multiple threads.

What is the purpose of `Thread.join()` in Java?

Answer: To make the current thread wait until the specified thread finishes

`Thread.join()` causes the calling thread to block until the thread on which `join()` was called completes its execution.

Which concurrent collection class is designed for high-concurrency scenarios and partitions its data to reduce lock contention?

Answer: ConcurrentHashMap

`ConcurrentHashMap` uses segment-level (or node-level in Java 8+) locking for better throughput than a fully synchronized map.