What information is transmitted and how does the Completable object interact in RxJava?

The Completable object in RxJava represents a stream that does not emit any data, but only signals successful completion or an error. It is used for operations where the result is not a value, but only the fact of completion (for example, writing to a database, sending a request).

Interaction with Completable occurs through three main events:

• onComplete() — the operation completed successfully.
• onError(Throwable e) — an error occurred.

Example of usage:

Completable.fromAction(() -> {
    // Some operation without a return result
    saveDataToDatabase();
})
.subscribe(
    () -> System.out.println("Operation completed successfully"),
    throwable -> System.err.println("Error: " + throwable.getMessage())
);

Thus, Completable is useful for asynchronous tasks where only the fact of completion or error matters, without data transfer.