Creating instances without new keyword in Kotlin - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an instance of the class without using the 'new' keyword.

Kotlin

class Person(val name: String)

val person = [1]("Alice")

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

Amake Person

Bnew Person

Ccreate Person

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' keyword which is not used in Kotlin.

Trying to use other keywords like 'create' or 'make'.

In Kotlin, you create instances by calling the class name like a function, without using the 'new' keyword.

2fill in blank

medium

Complete the code to instantiate the data class without 'new'.

Kotlin

data class Car(val model: String, val year: Int)

val car = [1]("Toyota", 2020)

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

ACar

BCar()

Ccreate Car

Dnew Car

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' keyword.

Calling the class with empty parentheses when parameters are required.

In Kotlin, you create an instance by calling the class name with arguments directly, no 'new' keyword needed.

3fill in blank

hard

Fix the error by completing the code to create an instance of the class without 'new'.

Kotlin

class Book(val title: String)

val book = [1]("Kotlin Guide")

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

ABook

Bnew Book

Ccreate Book

DBook()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' keyword.

Calling the class without required parameters.

Kotlin creates instances by calling the class name with parameters directly, no 'new' keyword.

4fill in blank

hard

Fill both blanks to create an instance of the class without 'new' and access its property.

Kotlin

class User(val username: String)

val user = [1]("john_doe")
println(user.[2])

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

AUser

Bname

Cusername

Dnew User

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' keyword to create instance.

Accessing a property name that does not exist.

Create the instance by calling the class name directly and access the property by its correct name.

5fill in blank

hard

Fill all three blanks to create an instance, call a method, and print the result without using 'new'.

Kotlin

class Calculator {
    fun add(a: Int, b: Int): Int = a + b
}

val calc = [1]()
val sum = calc.[2](5, 7)
println([3])

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

ACalculator

Badd

Csum

Dnew Calculator

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' keyword to create instance.

Calling a method name incorrectly.

Printing the wrong variable.

Create the instance by calling the class name directly, call the method by its name, and print the variable holding the result.

Practice

1. In Kotlin, how do you create an instance of a class named Car without using the new keyword?

easy

A. val myCar = Car()

B. val myCar = new Car()

C. val myCar = create Car()

D. val myCar = Car.new()

Solution

1. Step 1: Understand Kotlin instance creation

   Kotlin does not use the new keyword; instead, it calls the class name like a function.

2. Step 2: Apply correct syntax for creating instance

   To create an instance of Car, simply write Car() without new.

3. Final Answer:

   val myCar = Car() -> Option A

4. Quick Check:

   Kotlin instance creation = Car() [OK]

Hint: Remember: Kotlin uses class name with parentheses, no 'new' needed [OK]

Common Mistakes:

• Using 'new' keyword like in Java
• Trying to call a method like 'create Car()'
• Using 'Car.new()' which is invalid

2. Which of the following is the correct syntax to create an instance of class Person in Kotlin?

easy

A. val p = new Person()

B. val p = create Person()

C. val p = Person.new()

D. val p = Person()

Solution

1. Step 1: Recall Kotlin instance creation syntax

   Kotlin creates instances by calling the class name with parentheses, no 'new' keyword.

2. Step 2: Identify the correct syntax

   Only val p = Person() matches Kotlin's syntax for creating an instance.

3. Final Answer:

   val p = Person() -> Option D

4. Quick Check:

   Instance creation = ClassName() [OK]

Hint: Use ClassName() directly to create instances in Kotlin [OK]

Common Mistakes:

• Adding 'new' keyword before class name
• Using 'Person.new()' which is invalid
• Trying to use 'create' keyword

3. What will be the output of the following Kotlin code?

class Dog(val name: String) {
    fun bark() = "Woof! I am $name"
}

fun main() {
    val dog = Dog("Buddy")
    println(dog.bark())
}

medium

A. Woof! I am name

B. Woof! I am dog

C. Woof! I am Buddy

D. Compilation error

Solution

1. Step 1: Understand instance creation and property assignment

   The instance dog is created by calling Dog("Buddy"), setting name to "Buddy".

2. Step 2: Evaluate the bark() function output

   The bark() function returns the string with $name replaced by "Buddy".

3. Final Answer:

   Woof! I am Buddy -> Option C

4. Quick Check:

   dog.bark() = "Woof! I am Buddy" [OK]

Hint: Instance properties are set by constructor arguments [OK]

Common Mistakes:

• Expecting 'dog' or 'name' literal instead of property value
• Thinking Kotlin requires 'new' keyword
• Assuming compilation error due to syntax

4. Identify the error in the following Kotlin code snippet:

class Book(val title: String)

fun main() {
    val b = new Book("Kotlin Basics")
    println(b.title)
}

medium

A. Missing parentheses after class name

B. Using 'new' keyword which is invalid in Kotlin

C. Incorrect property access syntax

D. Class Book must be declared as data class

Solution

1. Step 1: Check instance creation syntax

   The code uses new Book("Kotlin Basics"), but Kotlin does not use the new keyword.

2. Step 2: Identify correct Kotlin syntax

   Instance creation should be Book("Kotlin Basics") without new.

3. Final Answer:

   Using 'new' keyword which is invalid in Kotlin -> Option B

4. Quick Check:

   Kotlin instance creation = ClassName() without 'new' [OK]

Hint: Remove 'new' keyword to fix instance creation error [OK]

Common Mistakes:

• Adding 'new' keyword from Java habits
• Thinking parentheses are optional
• Confusing data class requirement

5. Given the Kotlin class below, how can you create a list of Person instances without using the new keyword?

class Person(val name: String, val age: Int)

Choose the correct code snippet.

hard

A. val people = listOf(Person("Alice", 30), Person("Bob", 25))

B. val people = listOf(new Person("Alice", 30), new Person("Bob", 25))

C. val people = listOf(Person.new("Alice", 30), Person.new("Bob", 25))

D. val people = listOf(create Person("Alice", 30), create Person("Bob", 25))

Solution

1. Step 1: Understand Kotlin instance creation in collections

   Instances are created by calling the class name with parentheses, no 'new' keyword.

2. Step 2: Check list creation syntax

   listOf() accepts instances created by Person("Alice", 30) and Person("Bob", 25).

3. Final Answer:

   val people = listOf(Person("Alice", 30), Person("Bob", 25)) -> Option A

4. Quick Check:

   Instances in list = Person() calls without 'new' [OK]

Hint: Use ClassName() inside listOf() to create instances [OK]

Common Mistakes:

• Adding 'new' keyword inside listOf()
• Using invalid 'Person.new()' syntax
• Trying to use 'create' keyword