Classes and objects in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a class named Person.

Flutter

class [1] {
  String name;
  Person(this.name);
}

Drag options to blanks, or click blank then click option'

AAnimal

BPerson

CCar

DWidget

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name that does not match the constructor.

Choosing unrelated class names.

The class name should be Person to match the constructor and represent a person.

2fill in blank

medium

Complete the code to create an object of the Person class.

Flutter

var person = [1]('Alice');

Drag options to blanks, or click blank then click option'

AAnimal

BWidget

CPerson

DCar

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong class name to create the object.

Forgetting to add parentheses.

To create an object, use the class name Person followed by parentheses with arguments.

3fill in blank

hard

Fix the error in the method to return the person's name.

Flutter

class Person {
  String name;
  Person(this.name);

  String getName() {
    return [1];
  }
}

Drag options to blanks, or click blank then click option'

Athis.name

Bname()

CgetName

DPerson.name

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call name as a function.

Using class name to access instance variable.

Use this.name or simply name to access the instance variable inside the class.

4fill in blank

hard

Fill both blanks to add an age property and initialize it in the constructor.

Flutter

class Person {
  String name;
  int [1];

  Person(this.name, this.[2]);
}

Drag options to blanks, or click blank then click option'

Aage

Bheight

Cweight

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for property and constructor parameter.

Choosing unrelated property names.

The property and constructor parameter should both be named age to store the person's age.

5fill in blank

hard

Fill all three blanks to create a method that returns a greeting with the person's name and age.

Flutter

class Person {
  String name;
  int age;

  Person(this.name, this.age);

  String greet() {
    return 'Hello, my name is $[1] and I am $[2] years [3].';
  }
}

Drag options to blanks, or click blank then click option'

Aname

Bage

Cold

Dyears

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names.

Forgetting to use the word 'old' in the sentence.

The method uses name and age variables and the word old to form the greeting sentence.

Practice

1. What is a class in Flutter programming?

easy

A. A type of widget

B. A blueprint to create objects

C. A function that runs the app

D. A variable that stores data

Solution

1. Step 1: Understand the role of a class

   A class defines a template or blueprint for creating objects with properties and behaviors.

2. Step 2: Differentiate from other concepts

   Widgets, functions, and variables serve different purposes; only a class is a blueprint for objects.

3. Final Answer:

   A blueprint to create objects -> Option B

4. Quick Check:

   Class = blueprint for objects [OK]

Hint: Classes define blueprints, not widgets or variables [OK]

Common Mistakes:

• Confusing classes with widgets
• Thinking classes are functions
• Mixing classes with variables

2. Which of the following is the correct way to define a simple class named Car in Dart?

easy

A. function Car() { }

B. Car class { }

C. def Car() { }

D. class Car { }

Solution

1. Step 1: Recall Dart class syntax

   In Dart, classes are defined using the keyword class followed by the class name and curly braces.

2. Step 2: Check each option

   Only class Car { } uses the correct Dart syntax: class Car { }. Others use incorrect keywords or syntax.

3. Final Answer:

   class Car { } -> Option D

4. Quick Check:

   Dart class syntax = class Name { } [OK]

Hint: Use 'class' keyword followed by name and braces [OK]

Common Mistakes:

• Using 'def' or 'function' instead of 'class'
• Placing 'class' after the name
• Missing curly braces

3. What will be the output of this Dart code?

class Dog {
  String name;
  Dog(this.name);
  void bark() {
    print('Woof! My name is $name');
  }
}

void main() {
  var dog = Dog('Buddy');
  dog.bark();
}

medium

A. Woof! My name is Buddy

B. Woof! My name is dog

C. Error: Missing constructor

D. Nothing is printed

Solution

1. Step 1: Understand the class and constructor

   The class Dog has a constructor that sets the name property to 'Buddy'.

2. Step 2: Analyze the bark method call

   The bark() method prints 'Woof! My name is ' followed by the dog's name, which is 'Buddy'.

3. Final Answer:

   Woof! My name is Buddy -> Option A

4. Quick Check:

   dog.bark() prints name set by constructor [OK]

Hint: Constructor sets name; bark prints it [OK]

Common Mistakes:

• Assuming default constructor without parameters
• Forgetting string interpolation syntax
• Expecting no output without main()

4. Identify the error in this Dart class definition:

class Person {
  String name
  int age;

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

medium

A. Missing semicolon after 'String name'

B. Constructor syntax is wrong

C. Class name should be lowercase

D. No error, code is correct

Solution

1. Step 1: Check property declarations

   The line String name is missing a semicolon at the end, which is required in Dart.

2. Step 2: Verify constructor and class name

   The constructor syntax is correct, and class names start with uppercase by convention, so no error there.

3. Final Answer:

   Missing semicolon after 'String name' -> Option A

4. Quick Check:

   Every property line needs a semicolon [OK]

Hint: Check each line ends with a semicolon [OK]

Common Mistakes:

• Ignoring missing semicolons
• Thinking constructor syntax is wrong
• Confusing naming conventions with errors

5. You want to create a class Book that stores a title and author, and has a method describe() that returns a string like "Title by Author". Which code correctly implements this?

hard

A. class Book {
String title, author;
Book(this.title, this.author);
String describe() {
print('$title by $author');
}
}

B. class Book {
String title, author;
Book(this.title, this.author);
void describe() {
print('$title by $author');
}
}

C. class Book {
String title, author;
Book(this.title, this.author);
String describe() {
return '$title by $author';
}
}

D. class Book {
String title, author;
Book(this.title, this.author);
describe() {
print('$title by $author');
}
}

Solution

1. Step 1: Check method return type and behavior

   The method describe() should return a string, so its return type must be String and it must use return.

2. Step 2: Analyze each option

   class Book { String title, author; Book(this.title, this.author); String describe() { return '$title by $author'; } } correctly returns the string. class Book { String title, author; Book(this.title, this.author); void describe() { print('$title by $author'); } } returns void and prints instead of returning. class Book { String title, author; Book(this.title, this.author); String describe() { print('$title by $author'); } } returns String but uses print, which returns void. class Book { String title, author; Book(this.title, this.author); describe() { print('$title by $author'); } } omits return type and prints instead of returning a string.

3. Final Answer:

   class Book { String title, author; Book(this.title, this.author); String describe() { return '$title by $author'; } } -> Option C

4. Quick Check:

   Method returns string with return keyword [OK]

Hint: Use return with correct type for methods [OK]

Common Mistakes:

• Using print instead of return
• Omitting return type
• Returning void when string expected