Explain the differences between hot and cold data streams in reactive systems.

In reactive systems, data streams are divided into Hot and Cold depending on the behavior of the data source:

• Cold streams are streams that start generating data only after an observer subscribes to them. Each subscriber receives the full data stream from the beginning. Example — Observable in RxSwift, which starts emitting values upon subscription.

• Hot streams are streams that generate data regardless of the presence of subscribers. Subscribers receive data from the moment of subscription, skipping previous events. Example — user interface events (button clicks) that occur constantly.

Thus, Cold streams are lazy and individual for each subscriber, while Hot streams are active and shared among all subscribers.