What is Future<> in Dart?

In Dart, we can execute asynchronous code by using a variety of classes and keywords such as Future. A Future allows us to execute asynchronous programs.

Note: A program code can accomplish tasks while awaiting the completion of another action thanks to asynchronous operations.

A Future primarily represents the outcome of an asynchronous operation.

An asynchronous operation includes the following:

  1. Fetching data via a network
  2. Writing/reading files from cloud storage

In Dart, a Future has two states:

  1. Completed: When an asynchronous operation on a Future is finished, the Future successfully completes with a value. Otherwise, it completes unsuccessfully with an error.

  2. Uncompleted: When an asynchronous operation is called, it queues up and returns an unfinished Future.

Note: In Dart, the state of a Future before it has generated a value is referred to as being uncompleted.

Syntax

Future<T>

Return type

The return type is void if the Future does not yield any value.

Code

The following code shows how to use Future in Dart.

Example 1

// getWriterName function of type `Future` which computes a future
// the return type is String
Future<String> getWriterName() {
   // 3 seconds delay to simulate a call to cloud storage or db
   return Future.delayed(Duration(seconds: 3), () => "Maria Elijah");
}
void main() {
   print('Welcome to Educative!');
   var writerName = getWriterName();
   // create a callback
   writerName.then((name) => print("The writer's name is $name"));
   print('Keep Learning!');
}

Code explanation

Line 3-6: We create a function called getWriterName() of the Future type. This function computes a Future and returns a String.

Line 9: We define the main() function.

Line 10: We use print() to display a statement.

Line 11: We assign the getWriterName() function to a new variable called writername.

Line 13: We create a callback to display the Future value (in our case, the value is the writer’s name).

Line 14: We use print() to display a statement.

Note: The print() function on line 14 was executed before the callback because the getWriterName() function is an asynchronous operation.

Example 2

// displayGreetings function of type `Future` which computes a future
// the return type is void
Future<void> displayGreetings() {
   // 3 seconds delay to simulate a call to cloud storage or db
   return Future.delayed(Duration(seconds: 3), () => print('Welcome to Educative!'));
}
void main() {
  // call the future 
  displayGreetings();
  print('Keep Learning!');
}

Code explanation

Line 4-7: We create a function called displayGreetings() of the Future type. This function computes a Future and returns void.

Line 10: We define the main() function.

Line 11: We call the displayGreetings() function.

Line 13: We use print() to display a statement.

Free Resources

Copyright ©2025 Educative, Inc. All rights reserved