What is the difference between add, offer and put on a BlockingQueue?

Each operation comes in four flavours, and the javadoc's own table is worth having in your head:

	Throws	Returns a special value	Blocks	Times out
Insert	add(e)	offer(e)	put(e)	offer(e, time, unit)
Remove	remove()	poll()	take()	poll(time, unit)
Examine	element()	peek()

Which to use is a design decision about what should happen when the other side is slow. A producer that must not lose data and is allowed to wait uses put, which is backpressure. A producer that must never block, such as a request thread or an event loop, uses offer with a timeout and does something deliberate with false: shed the request, count it, return 503. add turns a full queue into an exception, which is rarely what you want.

On the consumer side, take waits forever and responds to interruption, while poll with a timeout lets a loop wake up regularly to check a shutdown flag. drainTo moves everything available in one lock acquisition, which is the cheap way to consume in batches.

Two details people miss: a BlockingQueue rejects null with a NullPointerException, because poll uses null to mean empty. And on an unbounded queue add and offer never fail, which is the unbounded-queue problem again: the backpressure you designed for never happens.