What is the purpose of the subscribeOn operator in working with Observable in reactive programming?

The subscribeOn operator in reactive programming is used to specify on which thread (Scheduler) the subscription to an Observable and its data source will occur. This means that all event generation logic will be executed on the specified thread, allowing control over multithreading and avoiding blocking the main UI thread.

For example, if you want to perform a network request in a background thread and process the result on the UI thread, subscribeOn specifies the thread for executing the request, and observeOn specifies the thread for processing the result:

observable
    .subscribeOn(Schedulers.io())       // execute in background thread
    .observeOn(AndroidSchedulers.mainThread()) // process on UI thread
    .subscribe(...);