Vispro Week 1 - OOP concept in DART

What is DART?

• programming language

• programming framework

• programming architecture

• programming paradigm ✅

What will be the type of x in the following Dart code?

• dynamic

• int

• Object

• num

Answer explanation

When declared with var, Dart infers the type from the first assignment. Here, x becomes int. If you want it to be truly dynamic, you must explicitly declare dynamic.

Which of the following correctly explains the difference between final and const in Dart?

• final can be set only once at runtime, const is a compile-time constant

• const can be reassigned, final cannot

• Both are identical

• final must always be declared with a value, const does not

Answer explanation

final is initialized once and can hold a runtime value. const must be assigned a compile-time constant.

What will this Dart code print?

• null

• Guest

• Compilation error

• Empty string

Answer explanation

Since name is nullable and currently null, the null-coalescing operator ?? provides "Guest" as the fallback.

Which scenario is the best use case for the late keyword in Dart?

• When you want to delay initialization of a non-nullable variable

• When you want to make a variable nullable

• When you want a compile-time constant

• When you want to create a global variable

Answer explanation

late is used when a non-nullable variable cannot be initialized immediately, but you guarantee it will be set before use.

The late keyword in Dart is used to declare a variable or field that will be initialized at a later time, specifically when it is first accessed. This keyword is particularly useful in the context of Dart's sound null safety, as it allows for the declaration of non-nullable variables without requiring immediate initialization. 

The primary use case for late is to declare non-nullable variables that cannot be initialized at the point of declaration. Without late, such variables would either need to be marked as nullable (using ?) or initialized immediately, which might not always be feasible.

What will this Dart code print?

• 42

• "hello"

• Compilation error

• dynamic

Answer explanation

A dynamic variable can change its type at runtime. Initially it is an int, then reassigned to a String.

In Dart, the dynamic keyword allows for the declaration of a variable whose type can change at runtime. This means a variable declared with dynamic can hold values of any type, and its type can be reassigned throughout its lifecycle. 

Runtime Type Flexibility:

Unlike var (which infers a type at compile-time and then restricts the variable to that type), dynamic truly allows the type to change during program execution.

• Reduced Type Safety:

  While offering flexibility, using dynamic sacrifices compile-time type checking. This means potential type-related errors might only be discovered at runtime, leading to less robust code compared to using specific types or var with type inference.
  

• Use Cases:

  dynamic is typically used when the exact type of a variable is genuinely unknown or when interoperating with external systems (like JSON parsing) where the data structure might be unpredictable.
  

• Best Practice:

  In general, it is recommended to use dynamic sparingly and only when necessary due to the reduced type safety. Prefer specific types or var with type inference for better code maintainability and error prevention.

What is the purpose of extension methods in Dart?

• To allow adding new methods to existing classes without modifying them

• To create subclasses dynamically

• To override private methods

• To replace inheritance

Answer explanation

Extension methods in Dart allow developers to add new functionalities to existing classes without modifying their original source code or using inheritance. This feature is particularly useful for extending the behavior of classes from core libraries or third-party packages that cannot be directly altered.

• Extension methods enable the addition of methods, getters, setters, and operators to a class as if they were part of its original definition.

What will be the output of the following code?

• 0

• null

• Compilation error

• Runtime exception

Answer explanation

The ? makes name nullable. Since it is uninitialized (null), name?.length evaluates to null.

Which of the following correctly declares a variable that will be initialized later but not nullable?

• late String name;

• String? name;

• String name;

• var name;

Answer explanation

late allows non-nullable variables to be initialized later (useful for dependency injection).

Which of the following best describes a mixin in Dart?

• A way to achieve multiple inheritance with state

• A way to reuse code across classes without inheritance

• A replacement for interfaces

• A type of abstract class

Answer explanation

Mixins allow code reuse across multiple classes without creating inheritance hierarchies.

Mixins are a way of defining code that can be reused in multiple class hierarchies. They are intended to provide member implementations en masse.

To use a mixin, use the with keyword followed by one or more mixin names.