Top Dart Interview Questions & Answers for 2024

Dart is a general-purpose object-oriented language that finds its applications mainly in mobile, web, and server app development. Developed at Google, Dart has surprisingly made its way to the mainstream because of its robust features, and is relatively easy to learn and strongly integrated with the Flutter framework for mobile app development.

Therefore, every fresher or experienced developer must understand the syntax of Dart to remain in a competitive position in this fast-changing tech world. Here is an article that gives you a complete list of Dart interview questions for freshers and experienced developers, to be ready for any kind of question that arises during the interview.

Dart Interview Questions For Beginners

1. What is a Dart?

Dart is a programming language designed for building mobile, web, and desktop applications. It is developed by Google and can also be used to build server applications.

2. What are the data types in Dart?

• Strings: String values are represented by the keyword String.
• Booleans: A Boolean value is represented by the bool keyword.
• Lists: Predefined List classes are used to describe lists.
• Maps: Predefined Map classes are used to describe Maps.
• The Dynamic Type: The dynamic keyword is explicitly used as a type annotation.

3. What are the Features of Dart?

Dart is a Class-Based, Object-Oriented Language with Single Inheritance that follows C Style Syntax.

• Lexical scoping, closures, and optional static types are also supported.
• Dart supports features such as refactoring, breakpoints, and virtual machines, and it comes with a Dart Editor and SDK for an integrated experience.
• Dart can be converted to javascript using the dart2js tool, which is extremely valuable because it allows it to work on all modern browsers with very little code and run on servers using the SDK's Virtual Machine.

4. What are the ways to execute a Dart Program?

The following are the methods for executing a Dart Program:

• Command-line
• Dart console applications

5. What are the different types of Dart applications?

It can be used to build various applications like mobile apps - with flutter, web apps, command line scripts as well as server-side applications.

6. What is the Dart SDK, and what does it include?

The SDK includes the libraries, command-line tools, and the Dart VM. It also includes tools like dartfmt for formatting code and dartdoc for generating documentation.

7. How does Dart handle memory management?

On the side of memory management, Dart uses the automatic reclamation of memory spaces that are no longer useful by garbage collectors.

8. What is the use of typedef in Dart?

In Dart, Typedef is used to generate a function's user-defined identity (alias). That identity can be used in place of the process in the program code. The function's parameters are defined using typedef. It can also provide the variable with a process.

9. Does Dart have a syntax for declaring interfaces?

Unlike other languages dart does not have any interface keyword, You can implement it with an abstract keyword

abstract class Joker{

void makePeopleLaugh();

}

class Clown implements Joker{

void makePeopleLaugh() {

// Here is where the magic happens

}

}

class Comedian implements Joker{

void makePeopleLaugh() {

// Here is where the magic happens

}

}

10. What is the difference between final and const?

Const: Value must be known at compile-time, const birthday = "2008/12/25" and it can't be changed after initialized.

Final: Value must be known at run-time, final birthday = getBirthDateFromDB() and it can't be changed after initialized.

11. What is sound null safe in dart?

Dart’s null safety is sound, which enables compiler optimizations. If the type system determines that something isn’t null, then that thing can never be null.

12. What is the late keyword used for?

In Dart, we use the late keyword to declare variables that will be initialized at a later point in time.

13. How to run the Dart application?

You can run any dart application by providing main as an entry method.

void main() {

for (int i = 0; i < 5; i++) {

print('hello ${i + 1}');

}

}

14. What “is” and “as” keywords in dart?

is keyword is used to check variable data type whereas “as” keyword is used to give alias name.

is Keyword

void main() {

dynamic a="test";

if(a is String){

print("string");

}

}

as Keyword

import 'package:flutter/material.dart' as m;

15. How do you catch an error in the Dart program?

Unlike other languages, dart try and catch syntax are different

try {

// ...

} on SomeException catch(e) {

//Handle exception of type SomeException

} catch(e) {

//Handle all other exceptions

}

16. What is the purpose of using the final keyword in Dart?

In Dart, the final keyword is used to declare a variable whose value cannot be changed once assigned. It is similar to const, but the value of a final variable can be determined at runtime. Using final allows you to ensure that a variable remains constant after its initialization, providing immutability and better performance in some cases.

17. What is a constructor? Name types of constructors in Dart.

A constructor is a special function of the class that is responsible for initializing the variables of the class.

There are three types of constructors in Dart as given below.

• Default Constructor or no-arg Constructor.
• Parameter Constructor.
• Named Constructor.

18. What Are The Various Types Of Operators In Dart?

There are many different types of operators in Dart:

• Arithmetic Operators
• Equality and Relational Operators
• Type test Operators
• Bitwise Operators
• Assignment Operators
• Logical Operators

19. What is the purpose of using the async and await keywords in Dart?

Async and await, in Dart, are key terms used in the domain of asynchronous programming. While dealing with functions involving potentially time-consuming operations, be it network requests or database access, it means the function returns a value or future that allows using the 'await' statement inside that function to wait for asynchronous operations in a non-blocking fashion to efficiently and responsively drive UI applications.

20.What is the purpose of the super keyword in Dart? Provide an example.

The super keyword in Dart is used to refer to the superclass or parent class. It allows accessing and invoking members (methods or properties) of the superclass from within a subclass. This is useful when the subclass wants to override a method but still needs to use the implementation from the superclass.

Example:

class Animal {

String name;

Animal(this.name);

void speak() {

print('Animal speaks');

}

}

class Dog extends Animal {

Dog(String name) : super(name);

@override

void speak() {

super.speak(); // Invoke the speak() method of the superclass

print('$name barks');

}

}

void main() {

var dog = Dog('Buddy');

dog.speak();

}

Code language: JavaScript (javascript)

In the example above, the Dog class extends the Animal class. By using super.speak() inside the speak() method of the Dog class, we invoke the speak() method of the Animal superclass before adding the custom behavior specific to the Dog class.

21. What are the differences between Object and dynamic?

dynamic is not a type; it just disables type checking. The object is the ‘union’ of all non-nullable types, type checking rules still apply.

With dynamic

// a 'dynamic' variable can be assigned value of any type

dynamic a = 2;

// assign 'dynamic' value to any variable and code checker will not complain

int b = a;

// even when there is a bug

String c = a;

With Object

// It is OK to assign a 'int' value to an 'Object' variable, because 'int' is a subtype of 'Object'

Object a = 2;

// will get type error: "A value of type 'Object' can't be assigned to a variable of type 'int'"

int b = a;

// typecast is required when assign a 'Object' value to a variale of one of its subtypes.

int c = a as int;

22. What is assert in dart?

assert statements are useful for debugging a dart project. It is used mainly in development mode. assert takes one expression and checks if it is true or false. If it is true, the program runs normally and if it is false, it stops the execution and throws one error called AssertionError.

23. What is Cascade notation in Dart?

Cascades (.., ?..) allow you to make a sequence of operations on the same object. In addition to accessing instance members, you can also call instance methods on that same object.

var paint = Paint()

..color = Colors.black

..strokeCap = StrokeCap.round

..strokeWidth = 5.0;

24. What is isolate?

To achieve concurrency dart, make use of isolate. Isolate is similar to multithread in other languages.

25. Is Method Overloading possible in Dart? If not, what is the alternative approach?

Dart doesn’t have overloading as it is our experience that overloading leads to confusion. Especially when you intend to override a method but accidentally overload it.

We can use optional arguments (named or not) as a better alternative.

Dart Interview Questions For Experienced

1. How do you handle exceptions in Dart?

Exceptions are handled using try, catch, and finally blocks. Use throw to raise an exception.

2. What is the isolate in Dart, and why is it important?

An isolate is a way to run code in a separate memory space, allowing for parallel execution. Isolates do not share memory, which avoids concurrency issues.

3. Explain the concept of “generics” in Dart and how they can be used to write reusable and type-safe code.

Generics in Dart provide a pathway to run generic, type-safe code but have different types without yielding static type checking. Using generics, classes, functions, and interfaces can be parameterized to work with a wide array of data types, facilitating code reuse and enhancing type safety.

The Dart Generics can be used to create classes or functions that work for a variety of types, yet they still catch type-related errors at compile time. The huge advantage of finding type defects early in the development cycle is that it reduces the possibilities for runtime errors, offering code robustness. Some major benefits of using generics in Dart are:

Code Reusability: By the implementation of generics, classes and functions can be developed in a way to support many types. Therefore, code reusability is enabled by eliminating this repetition of code for implementing the same logic on different types.

Type Safety: Naturally, generics provide type safety at compile time. Actually, the type parameters supplied to generic classes or functions are merely used by the compiler to perform certain static type checks. This would avoid type-related errors and ensure much more reliable code.

Abstraction: One of the abilities of generics is to achieve abstraction; in other words, the writability of the code is more generic in nature. More flexible and adaptive, this abstraction raises versatility and usability for the same code.

Performance Optimization: Another value addition that generics bring to the table is better performance because there won't be any type conversions or boxing/unboxing operations. The compiler will create, for each particular type, the corresponding version of the code, so when executed, it comes out optimized for the specific case.

Code readability: Generics make the code even more expressive or self-explanatory. Additional context is provided by the type parameters to the expected types, making it easier to read the code.

Such advantages make it a powerful tool in Dart to create reusable and type-safe code that can adapt itself to different types, improving maintainability, reliability, and performance.

4. What are the Snapshots in Dart?

The Dart relies heavily on snapshots. Snapshots are files that include objects and other runtime information.

Script snapshots
Snapshot files can be created from Dart programs. All of the program code and dependencies are prepared and ready to run in these folders. This enables quick start-ups.

Full snapshots
The Dart core libraries can be compiled into a snapshot file, allowing them to be loaded quickly. The core libraries are prebuilt snapshots that are loaded at runtime in most standard distributions of the main Dart

Object snapshots
Dart is an asynchronous programming language. For concurrency, it takes advantage of isolates. Because these are message-passing workers, a mechanism to serialize a message is required. This is accomplished by creating a snapshot from a particular object, which is then passed to another isolate for deserialization.

5. What is Dart Strings?

A sequence of characters is represented by the String data type. A Dart string is made up of UTF 16 code units in a specific order. Single, double, or triple quotes can be used to represent string values in Dart. Single or double quotations are used to denote single-line strings. Multi-line strings are represented by triple quotations.

6. How do you define and use an enumeration (enum) in Dart?

Enumerations are defined using the enum keyword and can be used to represent a fixed set of values.

7. What is the difference between async and async* in Dart function declarations?

async is used for asynchronous functions that return a single value or null, while async* is used for asynchronous generator functions that yield multiple values.

8. What are the supplementary packages published by Dart?

Many necessary supplemental packages are available from the Dart team, including:
Characters: Characters, also known as Unicode (extended) grapheme clusters, are strings seen as sequences of user-perceived characters. The Characters class provides access to a string's feelings and a mechanism to move between them using a CharacterRange.

Intl: Intl is the most important library. It declares the Intl class, the default locale, and methods for interacting with most internationalization processes. The DateFormat, NumberFormat, and BidiFormatter classes are also defined in this package.

HTTP: This package includes a collection of high-level methods and classes for consuming HTTP resources. It's cross-platform, with mobile, desktop, and browser support. The top-level functions provide the most convenient access to this library.

Crypto: A collection of cryptographic hashing methods written entirely in Dart in a single input digest. It can Invoke the convert method on the sha1, sha256, or md5 objects to hash a list of bytes.

Markdown: Markdown library is a Dart-based portable. On both the client and the server, it can parse Markdown into HTML. A few Markdown extensions are supported and provided in the initial Perl Markdown implementation. The ones that CommonMark supports are activated by default.

9. What is Lambda Function?

• Lambda is a short way to represent tiny functions.
• Arrow functions and lambda functions are both terms for the same thing.
• However, keep in mind that you can only return one expression with the Lambda function syntax. It can only be a single-line expression. A lambda function cannot run a block of code, just like a regular function.
• To summarise, if your function only returns one expression, you can use the lambda function to quickly represent it in only one line.
• Example:
  void main() {
  printMsg();
  print(test());
  }
  printMsg()= >
  print("hello");
  int test()= 123;
  // returning function

10. What are Getters and Setters?

The class methods getter and setter interpret data in class fields. A setter is used to set the class field’s data to some variable, whereas a getter is used to read or get the data of the class field.

Getter method
It's used to get a specific class field and save it in a variable. The default getter function is available in all classes, although it can be changed explicitly. The getter method is defined as follows:

return_type get field_name{

. . .

}

Setter method
It's used to put data into a variable that the getter method has returned. A default setter function exists for all classes, but it can be explicitly overridden. Using the set keyword, the setter method can be defined as:

set field_name{

. . .

}

11. How do you optimize a Dart application for performance?

Optimizing a Dart application for performance involves a few different steps.

Most importantly, you need to ensure your code is well-structured and efficient. This means there are no pieces of code that are redundant and the algorithms that are in place are the most efficient in completing the tasks in your hands, and lastly, the data structures in use are also very efficient. Lastly, be sure that your code is well-documented and easy to read.

Second, use the Dart compiler in code optimization. The Dart compiler optimizes certain patterns in your code. This includes loop unrolling and inlining. You can also profile your application using the Dart Observatory to find areas where it can be improved.

Third, you should use the Dart VM to optimize your application. The Dart VM can optimize your code for both speed and memory usage. You can also use the Dart VM to enable garbage collection, which can help reduce memory usage.

Finally, you should use the Dart SDK to optimize your application. There are a series of tools provided within the Dart SDK that will line up in optimizing your application. These include the dart2js compiler and the dart2native compiler. This really allows you to optimize your code for both speed and memory usage.

With these steps, you can optimize your Dart application for performance.

12. What is the difference between a function and a method in Dart?

The main difference between a function from a method in Dart would be that a function is a code block that stands alone and can be called from any part of a program, yet a method, however, is a function bound to a class or object. It can also be said that a method is a function defined inside a class and therefore can only be called within that particular class.

A function is declared by use of the keyword 'function', followed by the function name; it will take parameters. A method will be declared with the keyword 'method', followed with the name of the method, which shall take parameters.

A function is called to return some value or to print. A method does something with an object, like setting one of its properties or calling another method on it.

In Dart, functions and methods are first-class citizens. This means that functions and methods can be passed as arguments to other functions and methods and returned from functions and methods.

13. How do you handle memory management in Dart?

Dart uses Garbage Collection to perform memory management. Thus, memory management is automatically done. The Garbage Collector is responsible for reclaiming memory linked with an object that is not required when it is not needed. Memory is, therefore, not wasted, and the application runs efficiently.

The garbage collector avoids memory leakage. Memory leakage arises when an object is not necessary, yet the collected memory remains associated with it. In a correct way, it will not make the program run out of memory and therefore crash.

It frees up the memory space and enhances the performance of an application.By re-collecting memory taken by useless objects, the Garbage Collector can contribute to diminishing the amount of memory to be allocated for new objects. In this way, it supports the better performance of an application.

Finally, the garbage collector is run to ensure that the objects are destroyed once they are no longer in use. This may keep the memory from corruption and other sorts of problems that come due to poor memory management.

14. How do you work with Futures in Dart?

In Dart, a Future is an object that represents a delayed computation. A Future can be in one of three states: unfulfilled, fulfilled, or rejected. The Future class is used in the creation of Futures and the then and catchError methods, which handle the outcome of a Future.

Here's an example of how to work with Futures in Dart:

Future<String> fetchData() async {

var response = await http.get('https://example.com/data');

return response.body;

}

void main() {

fetchData().then((data) => print(data))

.catchError((error) => print("An error occurred: $error"));

}

In this example, the fetchData function returns a Future that will be fulfilled with the response body of an HTTP request. The then method is used to handle the successful outcome of the Future and the catchError method is used to handle any errors that might occur.

15. What is the purpose of the Mirror class in Dart?

The Mirror class in Dart is one of the most powerful tools any developer aiming to access the internal structure of a Dart program would avail themselves of. It allows access to private fields, methods, and constructors of a class and creation of new instances among other things. It also grants the developer high ability for type instance inspection and allows one to call a method over an object without having to know its type. This enables one to write rather dynamic and flexible code that can create objects of different types during runtime. Another application of the class Mirror is in debugging. It comes in handy when you want to inspect the state expressed by an object at any time.

16. How do you use the listen and cancel methods in Stream?

In Dart, using a Stream one has to use a listen method to start listening and a cancel to stop listening.

The following is an example using the listen and cancel methods in Stream:

Stream<int> countStream() {

return Stream.periodic(Duration(seconds: 1), (i) => i)

.take(5);

}

var subscription = countStream().listen((data) {

print(data);

});

// later

subscription.cancel();

In this example, the countStream function returns a stream that emits an increasing integer every second for a total of 5 times. It calls the listen method to start listening to the stream, and callback print(data) is executed for every emission of the new value. The subscription variable will hold a reference to the subscription and can later be used to stop listening to the stream by calling the cancel method on it.

It should also be noted that the listen method returns a StreamSubscription object. This can further help in suspending and resuming the stream with the respective pause and resume methods.

17. How do you handle real-time data streams in a Flutter application?

In a Flutter app, streams of real‐time data are managed with the StreamBuilder widget. The StreamBuilder widget becomes a parent of all widgets that need to be rebuilt when a new value is emitted on the Provided Stream.

Here is an example of StreamBuilder Widget implementation in Flutter for handling real‐time data streams in an application:

Stream<int> countStream() {

return Stream.periodic(Duration(seconds: 1), (i) => i);

}

StreamBuilder<int>(

stream: countStream(),

builder: (BuildContext context, AsyncSnapshot<int> snapshot) {

if (snapshot.hasError) {

return Text("An error occurred: ${snapshot.error}");

}

if (!snapshot.hasData) {

return CircularProgressIndicator();

}

return Text("Count: ${snapshot.data}");

},

)

In this example, countStream returns a stream that emits an increasing integer every second. It recreates the widget tree. This StreamBuilder widget takes a stream and rebuilds the widget tree every time a new value is emitted. The executed builder callback would be checked during the rebuilding of the widget in case of an error or if the data is not available. In case of an error, it shows an error message; if the data is not available, a loading indicator; otherwise, it displays a count.

18. How do you implement interoperability between Dart and JavaScript in a Flutter application?

One intrinsic solution that provides interoperability between Dart and JavaScript in a Flutter application is the Dart: js library. The dart: js library enables us to call a JavaScript function in Dart and vice versa directly. Below is a practical example of calling a JavaScript function from Dart using the dart: js library.

import 'dart:js' as js;

void callJSFunction() {

var result = js.context.callMethod("myJsFunction", ["Hello from Dart!"]);

print(result);

}

In this example, the callJSFunction function is called from Dart and it calls the JavaScript function myJsFunction passing the string "Hello from Dart!" as an argument. The callMethod method returns the result of the JavaScript function, which can be saved in the result variable and printed.

To call the Dart function from javascript you can use js.allowInterop(function) and call it like any other javascript function.

Implementing interoperability between Dart and JavaScript in a Flutter application allows you to leverage the strengths of both languages and build robust and efficient applications.

19. Explain the difference between synchronous and asynchronous programming in Dart.

20. Explain the concept of the const keyword in Dart and how it is used.

In Dart, a const keyword is used for declaring compile-time constants. These values must be known at compile time themselves and can never change while the program is running.

• Constant values are evaluated and initialized at compile time, their values lying in memory as part of the program code.
• Const values are primarily used for literal values like numbers, strings, or Boolean values, and even for immutable data structures and objects.

21. What are annotations in Dart, and how are they used?

Metadata in Dart, which carries extra information about classes, functions, variables, and other language elements, is known as an annotation. They may be used to denote semantic meaning, document code, or even to provide instructions to tools and libraries.

It has inbuilt annotations like @override and @deprecated, but also supports custom annotations that allow the developers to define their metadata and use them to annotate code.

Usually, annotations are used for tasks like code documentation, code analysis, and generation of code in Dart applications.

22. What are mixins in Dart, and how are they used for code reuse?

Mixins give the power of code reuse across a number of classes without needing to use inheritance. It provides a way to give functionality to a class by mixing in one or more mixins, aggregations of methods, and properties. It uses the "with" keyword in the class declaration and represents code reuse and modularity in such a way that developers may compose classes from reusable components.

23. What is the purpose of the assert keyword in Dart, and how is it used for debugging?

The assert keyword in Dart forces some conditions during development by throwing an AssertionError in case the condition gets evaluated as false. It is commonly used for debugging purposes to validate assumptions, check invariants, and detect logical errors in code. Assertions are typically enabled during development and testing but disabled in production to improve performance.

24. Explain the concept of the spread operator (…) in Dart and how it is used.

The spread operator (…) in Dart expands the elements of a collection or iterable into another collection or iterable. It allows developers to concatenate or merge multiple collections into a single collection or pass individual elements of a collection as arguments to a function or constructor. The spread operator is commonly used for tasks like list manipulation, collection initialization, and function invocation in Dart applications.

25. What are the common challenges faced while developing with Dart and how do you overcome them?

These include asynchronous operations handling, control of state in Flutter, optimization of performance, and code readability. Defeat these with best practices, proper state management solutions, analyzing performance with its optimization, and writing clean, well-documented code.

Conclusion

Any developer who is interested in developing high-performance and scalable apps should master Dart, especially now that Flutter is also gaining fast popularity for cross-platform development. The following will help one to be confident during any kind of Dart-based job interview, since these questions cover a very broad range of topics, from the most basic syntax to advanced concepts. Remember to deeply understand each single concept, practice coding regularly, and keep yourself updated with new developments around the Dart ecosystem. Good luck with your interview preparation!

FAQs:

What is the best way to prepare for a Dart programming interview?

To crack a programming interview in Dart, you first need to really understand all the nooks and corners of the Dart language itself. This begins with syntax and goes into data types, collections, error handling, etc. Practice problems in coding : LeetCode, HackerRank, or some other such site.On top of that, go through the common interview questions and study the Dart documentation. Also, work out small projects to get practical experience in applying what you have learned.

How important is Dart for Flutter development?

Dart lays the base for Flutter development because it is the programming language needed to build Flutter apps. Anyway, knowing Dart is important to apply the component elements and powers of Flutter effectively in any situation. By learning Dart, you will be able to solve problems related to how to write an efficient, maintainable, and scalable Flutter application. This means the full power of this framework will let you build mobile applications across platforms.

What are some common mistakes to avoid in Dart interviews?

Common mistakes to avoid in Dart interviews include:

• Not having a strong grasp of Dart fundamentals, such as data types, collections, and control flow.
• Ignoring the importance of writing clean, readable, and maintainable code.
• Failing to handle edge cases and error conditions properly in your solutions.
• Overlooking performance considerations, such as inefficient algorithms or excessive memory usage.
• Not being able to explain your thought process and the reasoning behind your coding decisions.

How can I improve my Dart coding skills?

Improving your Dart coding skills involves a combination of practice and study:

• Regularly solve coding problems and challenges on online platforms.
• Build small projects or contribute to open-source Dart projects to gain hands-on experience.
• Read the official Dart documentation and follow tutorials to deepen your understanding of the language.
• Participate in coding communities and forums to learn from others and stay updated on best practices.
• Review and refactor your code to improve its efficiency and readability.

Are there any specific Dart projects I should work on for better interview preparation?

Working on specific Dart projects can help you gain practical experience and prepare for interviews. Consider these types of projects:

• Create a simple CRUD (Create, Read, Update, Delete) application so you learn how to deal with data handling and state management.
• Write a small command-line utility or tool to automate, mainly, using Dart standard library features.
• Develop simple Flutter apps, for example, Todo and Weather applications, to elaborate on the integration of Dart with Flutter.
• Develop common algorithms and data structures in Dart to give flexibility in solving problems.
• Make contributions to open source Dart or Flutter projects to get experience on collaborative coding and learn from more experienced professionals.