What are the similarities and differences of Future and Stream?

Similarities between Future and Stream:

  1. Asynchronous Operations: Both Future and Stream are used to handle asynchronous operations in Dart and Flutter. They allow developers to perform non-blocking tasks efficiently.
  2. Completion States: Both Future and Stream have completion states that represent successful completion, failure, or an ongoing operation.
  3. Asynchronous Methods: Both Future and Stream provide methods to handle the results of asynchronous operations. For Future, we use .then() to handle the success and .catchError() to handle errors. For Stream, we use .listen() to subscribe to data events and .onError() to handle errors.
  4. Error Handling: Both Future and Stream allow you to handle errors that may occur during asynchronous operations.

Differences between Future and Stream:

  1. Single Value vs. Multiple Values:
    • Future: Represents a single value or an error that will be available at some point in the future. It provides a single result and completes after producing the result.
    • Stream: Represents a sequence of values or an error that can be continuously produced over time. It allows multiple values to be emitted over time, potentially infinite.
  2. Completion:
    • Future: A Future can only be completed once with a single value or an error. Once completed, it cannot be modified or updated with new data.
    • Stream: A Stream can emit multiple values over time, allowing continuous data flow. It can be closed when no more data needs to be emitted.
  3. Usage:
    • Future: Typically used when you expect a single value or the result of an operation that will complete in the future.
    • Stream: Typically used when you expect continuous or multiple values over time, such as event streams, data streams from network connections, or user input streams.
  4. Subscription:
    • Future: Once you register a callback with .then() or .catchError() on a Future, it will execute once when the Future is completed. You cannot listen for multiple events.
    • Stream: You can subscribe to a Stream using .listen() to continuously receive data events as they occur, allowing you to handle multiple values over time.

Example of Future:

Future<void> fetchData() {
  return Future.delayed(Duration(seconds: 2), () => print('Data from Future'));

void main() {
  fetchData().then((_) => print('Future completed'));
  print('Waiting for Future...');

Example of Stream:

import 'dart:async';

Stream<int> countStream() {
  return Stream.periodic(Duration(seconds: 1), (count) => count).take(5);

void main() {
  countStream().listen((count) => print('Count: $count'),
      onError: (error) => print('Error: $error'),
      onDone: () => print('Stream completed'));

In this example, fetchData() returns a Future that completes after a delay of 2 seconds, simulating an asynchronous operation. In the Stream example, countStream() emits integers every second using Stream.periodic. The listen() method is used to subscribe to the stream and receive multiple values over time.

In summary, Future and Stream both handle asynchronous operations in Dart and Flutter, but they differ in the number of values they produce and how they are consumed. Use Future when you expect a single result, and use Stream when you expect continuous or multiple values over time.

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