Top 23 Dart Interview Questions and Answers

Question

1. What is Dart?

Answer 1

Dart is an object-oriented programming language to develop apps for mobile, web, desktop and server applications. Dart has syntax similar to C and it's a class based, garbage collected programming language. Code written into Dart can be compiled to native machines codes or JavaScript code by Dart native compilers. Dart is developed and maintained by Google.

Answer 2

Sound null safety is a feature introduced in Dart 2.12 that aims to prevent null reference exceptions at runtime. It enforces strict rules for handling nullable types. With sound null safety, variables must be explicitly marked as nullable (?) or non-nullable. This helps catch potential null errors during compilation rather than at runtime.
Example:


// Before Dart 2.12 (nullable types)
String? name = null; // Nullable string, can hold null value

// With sound null safety (Dart 2.12+)
String? nullableName = 'John'; // Nullable string, can hold null value
nullableName = null; // Allowed because it's nullable

String nonNullName = 'Jane'; // Non-nullable string, cannot hold null value
nonNullName = null; // Error: Null safety violation, cannot assign null to a non-nullable variable

Answer 3

Dart provides built-in support for asynchronous programming using Futures and async/await syntax. A Future represents a potential value that may be available in the future, often the result of an asynchronous operation. The async keyword is used to mark a function as asynchronous, allowing it to use the await keyword to pause execution until a Future completes.
Example:


Future fetchData() {
  return Future.delayed(Duration(seconds: 3), () => 'Data fetched');
}

void main() async {
  print('Before fetching data');
  String data = await fetchData(); // Pauses execution until fetchData() completes
  print('After fetching data: $data');
}

In this example, fetchData() returns a Future that completes after a 3-second delay. The await keyword is used to pause the execution of the main() function until the Future completes, and the result is stored in the data variable.

Answer 4

Isolates in Dart are lightweight, independent workers that do not share memory. They provide a way to achieve concurrency and parallelism in Dart code while avoiding the complexities and potential issues associated with shared-memory threading. Unlike threads, isolates communicate through message passing, making them more suitable for distributed computing scenarios.
Example:


import 'dart:isolate';

void main() {
  Isolate.spawn(heavyComputation, messagePort.sendPort);
}

void heavyComputation(SendPort sendPort) {
  // Perform CPU-intensive computation
  sendPort.send('Computation completed');
}

In this example, the main() function spawns a new isolate by calling Isolate.spawn() and passing the heavyComputation function and a SendPort for communication. The heavyComputation function runs in the new isolate and can perform CPU-intensive tasks without blocking the main isolate. Communication between isolates is done via message passing using SendPort and ReceivePort.

Answer 5

Mixins in Dart are a way to reuse code from other classes without using traditional inheritance. A mixin is a class-like entity that can be "mixed in" with other classes to add or override functionality. Mixins provide a more flexible and composable approach to code reuse compared to single inheritance. They allow you to combine behavior from multiple sources without the constraints of the class hierarchy.
Example:


mixin CanFly {
  void fly() {
    print('Flying high');
  }
}

class Bird with CanFly {
  // Other Bird class members
}

class Airplane with CanFly {
  // Other Airplane class members
}

In this example, the CanFly mixin defines a fly() method. The Bird and Airplane classes both use the CanFly mixin by including with CanFly. This allows them to inherit the fly() method without being in a parent-child relationship. Mixins provide a more flexible and composable approach to code reuse compared to single inheritance.

Answer 6

Dart supports reflective programming through its mirror library, which provides a way to inspect and interact with code at runtime. Reflection allows you to access metadata about classes, methods, and fields, as well as invoke methods and access properties dynamically. Some use cases for reflection in Dart include serialization, dependency injection, and dynamic code generation.
Example:


import 'dart:mirrors';

class Person {
  String name;
  int age;

  Person(this.name, this.age);
}

void main() {
  var instance = Person('John', 30);
  var mirror = reflect(instance); // Create a mirror for the instance

  print(mirror.type.simpleName); // Person
  print(mirror.getField(#name).reflectee); // John
  print(mirror.getField(#age).reflectee); // 30
}

In this example, the reflect() function creates a mirror for the Person instance. The mirror provides access to metadata about the instance, such as its type and field values. This can be useful for tasks like serialization, dynamic code generation, or dependency injection.

Answer 7

Both const and final are used to define immutable variables in Dart, but they differ in their initialization behavior. const variables are compile-time constants, meaning their values must be known at compile-time. final variables, on the other hand, can be initialized at runtime, but their value cannot be changed once assigned. You would use const for values that can be determined at compile-time (e.g., constants, literals) and final for values that need to be computed or assigned at runtime.
Example:


const PI = 3.14159; // Compile-time constant
const List immutableList = [1, 2, 3]; // Immutable list

final now = DateTime.now(); // Runtime constant
final List mutableList = [4, 5, 6]; // Can modify list contents

Answer 8

Extensions in Dart allow you to add functionality to existing classes without modifying their source code or using inheritance. They are similar to mixins in that they provide a way to reuse code, but extensions operate on existing classes rather than defining new classes. Extensions are particularly useful when working with third-party libraries or classes that you cannot modify directly.
Example:


extension NumberParsing on String {
  int parseInt() {
    return int.parse(this);
  }
}

void main() {
  print('42'.parseInt()); // 42
}

In this example, the NumberParsing extension adds a parseInt() method to the String class. This method can then be called on any string, as shown in main(). Extensions differ from mixins in that they operate on existing classes rather than defining new classes. They are particularly useful when working with third-party libraries or classes that you cannot modify directly.

Answer 9

Dart supports generic programming through the use of type parameters. Generics allow you to define classes, interfaces, and methods that can work with different types while maintaining type safety. This promotes code reusability and avoids the need for explicit type casting or runtime type checks. Generics also enable better tooling support, such as code completion and static analysis.
Example:


class Box {
  T content;

  Box(this.content);
}

void main() {
  Box numberBox = Box(42); // Box containing an integer
  Box stringBox = Box('Hello'); // Box containing a string
}

In this example, a type parameter T is used to define the Box class. This allows creating instances of Box that hold different types, such as Box of int and Box of String. Generics promote code reusability and maintain type safety, avoiding the need for explicit type casting or runtime type checks. They also enable better tooling support, like code completion and static analysis.

Answer 10

represent asynchronous sequences of data. They can be used to implement reactive programming patterns, where data flows through a series of transformations and listeners. Streams can be created from various sources, such as user input, file I/O, or network requests, and they support operations like mapping, filtering, and combining. Streams are widely used in Dart for building responsive and event-driven applications.
Example:


Stream countStream() async* {
  for (int count = 1; count <= 10; count++) {
    yield count;
    await Future.delayed(Duration(seconds: 1));
  }
}

void main() {
  countStream().listen((count) {
    print('Received: $count');
  });
}

In this example, the countStream() function is an asynchronous generator that yields integers from 1 to 10, with a 1-second delay between each value. The main() function listens to the stream using the listen() method, which executes a callback function for each received value. Streams are widely used in Dart for reactive programming patterns, where data flows through a series of transformations and listeners.

Answer 11

The dart:ffi library provides a Foreign Function Interface (FFI) for Dart, allowing you to call native C functions from Dart code and vice versa. This is particularly useful when you need to interact with existing native libraries or system APIs that are not available in Dart's standard libraries. The FFI can be used for tasks like system programming, hardware integration, or interoperability with legacy code.
Example:


import 'dart:ffi';
import 'dart:io';

final dynaLib = Platform.isWindows
    ? DynamicLibrary.open('user32.dll')
    : DynamicLibrary.process();

final messageBoxA = dynaLib.lookupFunction, Pointer, Uint32), int Function(int, Pointer, Pointer, int)>('MessageBoxA');

void main() {
  final titlePtr = 'Hello'.toNativeUtf8();
  final messagePtr = 'This is a message box'.toNativeUtf8();
  messageBoxA(0, messagePtr, titlePtr, 0);
  free(titlePtr);
  free(messagePtr);
}

Answer 12

For Dart tutorials visit Dart Tutorials

Answer 13

When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like Dart, So It's depend on your knowledge and work experience in Dart. The interviewer expects a realistic self-evaluation aligned with your qualifications.

Answer 14

The challenges faced while working on Dart projects are highly dependent on one's specific work experience and the technology involved. You should explain any relevant challenges you encountered related to Dart during your previous projects.

Answer 15

This question is commonly asked in interviews to understand your specific responsibilities and the functionalities you implemented using Dart in your previous projects. Your answer should highlight your role, the tasks you were assigned, and the Dart features or techniques you utilized to accomplish those tasks.

Answer 16

Here you can tell about your overall work experience on Dart.

Answer 17

Whether a candidate has completed any Dart certification or training is optional. While certifications and training are not essential requirements, they can be advantageous to have.

Answer 18

We have covered some frequently asked Dart Interview Questions and Answers to help you for your Interview. All these Essential Dart Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any Dart Interview if you face any difficulty to answer any question please write to us at info@qfles.com. Our IT Expert team will find the best answer and will update on the portal. In case we find any new Dart questions, we will update the same here.

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Top 23 Dart Interview Questions and Answers

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