Why Kotlin is the official Android language in Android Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple Kotlin function that prints a greeting.

Android Kotlin

fun greet() {
    println([1])
}

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

A"Hello, Android!"

BHello, Android!

Cprintln("Hello, Android!")

Dprint("Hello, Android!")

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string

Trying to call print inside println

The println function requires a string argument in quotes to print text. So, "Hello, Android!" is correct.

2fill in blank

medium

Complete the code to declare a Kotlin variable that cannot be changed.

Android Kotlin

val language: String = [1]

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

A"Kotlin"

BKotlin

Ckotlin

D'Kotlin'

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes instead of double quotes

Not using quotes at all

String values must be in double quotes in Kotlin. val means the variable is read-only.

3fill in blank

hard

Fix the error in the Kotlin function that returns the length of a string.

Android Kotlin

fun lengthOf(text: String): Int {
    return text.[1]
}

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

Alength()

Bcount()

Csize()

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using length() with parentheses causes an error

Using size() which is not a String property

In Kotlin, String length is a property accessed without parentheses: text.length

4fill in blank

hard

Fill both blanks to create a Kotlin list and print its size.

Android Kotlin

val fruits = listOf([1])
println(fruits.[2])

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

A"Apple", "Banana", "Cherry"

Bsize()

Csize

D"Apple"

Attempts:

3 left

💡 Hint

Common Mistakes

Using size() with parentheses causes error

Passing a single string instead of multiple elements

listOf takes elements as arguments. size is a property to get the list length.

5fill in blank

hard

Fill all three blanks to create a Kotlin data class and instantiate it.

Android Kotlin

data class [1](val name: String, val age: Int)
val person = [2]([3], 30)

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

APerson

BPerson()

C"Alice"

Attempts:

3 left

💡 Hint

Common Mistakes

Using Person() as class name

Not using quotes around the string argument

Define data class Person, then create instance with Person("Alice", 30).

Practice

1. Why did Google choose Kotlin as the official language for Android development?

easy

A. Because Kotlin requires more code than Java

B. Because Kotlin is the oldest programming language

C. Because Kotlin is modern, safe, and concise

D. Because Kotlin is only used for web development

Solution

1. Step 1: Understand Google's criteria for Android languages

   Google wanted a language that is modern, safe, and concise to improve developer productivity.

2. Step 2: Match Kotlin's features to these criteria

   Kotlin is modern, reduces boilerplate code, and has safety features like null safety.

3. Final Answer:

   Because Kotlin is modern, safe, and concise -> Option C

4. Quick Check:

   Kotlin's modern features = official Android language [OK]

Hint: Remember: official means modern, safe, concise [OK]

Common Mistakes:

• Thinking Kotlin is old or outdated
• Confusing Kotlin with JavaScript
• Believing Kotlin requires more code

2. Which of the following is the correct way to declare a variable in Kotlin?

easy

A. dim name as String = "Android"

B. string name = "Android";

C. let name = "Android"

D. var name: String = "Android"

Solution

1. Step 1: Recall Kotlin variable declaration syntax

   Kotlin uses var or val followed by variable name, colon, type, and assignment.

2. Step 2: Identify the correct syntax among options

   var name: String = "Android" matches Kotlin syntax exactly; others are from different languages.

3. Final Answer:

   var name: String = "Android" -> Option D

4. Quick Check:

   Kotlin variable declaration = var name: Type = value [OK]

Hint: Kotlin uses var or val with colon for type [OK]

Common Mistakes:

• Using JavaScript or Swift syntax by mistake
• Forgetting the colon before the type
• Adding semicolons at the end

3. What will be the output of this Kotlin code snippet?

fun main() {
  val name: String? = null
  println(name?.length ?: "No name")
}

medium

A. No name

B. 0

C. null

D. Throws NullPointerException

Solution

1. Step 1: Understand the safe call and Elvis operator

   The ?. safely accesses length only if name is not null; otherwise returns null. The Elvis operator ?: provides a default value.

2. Step 2: Apply to given code

   Since name is null, name?.length is null, so the Elvis operator returns "No name".

3. Final Answer:

   No name -> Option A

4. Quick Check:

   Safe call + Elvis operator = "No name" output [OK]

Hint: Safe call ?. with ?: gives default if null [OK]

Common Mistakes:

• Expecting NullPointerException
• Thinking null prints as string
• Confusing safe call with normal call

4. Identify the error in this Kotlin code snippet:

fun main() {
  val number: Int = null
  println(number)
}

medium

A. Cannot assign null to non-nullable type Int

B. Missing semicolon after println

C. Variable number should be declared with var instead of val

D. println function is not defined

Solution

1. Step 1: Check variable type and assignment

   The variable number is declared as non-nullable Int, but assigned null.

2. Step 2: Understand Kotlin null safety rules

   Non-nullable types cannot hold null; to allow null, type must be Int?.

3. Final Answer:

   Cannot assign null to non-nullable type Int -> Option A

4. Quick Check:

   Non-nullable Int cannot be null [OK]

Hint: Non-nullable types cannot hold null [OK]

Common Mistakes:

• Thinking val vs var causes error
• Expecting missing semicolon error
• Assuming println is undefined

5. How does Kotlin help Android developers write better apps faster compared to Java?

hard

A. By requiring more boilerplate code and manual null checks

B. By providing concise syntax, null safety, and full Google support

C. By limiting features to only basic programming constructs

D. By removing support for Android Studio and Gradle

Solution

1. Step 1: Identify Kotlin advantages over Java

   Kotlin reduces boilerplate code, has built-in null safety, and is fully supported by Google.

2. Step 2: Compare options to these advantages

   By providing concise syntax, null safety, and full Google support correctly lists these benefits; others are incorrect or opposite.

3. Final Answer:

   By providing concise syntax, null safety, and full Google support -> Option B

4. Quick Check:

   Kotlin's concise syntax + safety + support = faster better apps [OK]

Hint: Kotlin = concise + safe + Google supported [OK]

Common Mistakes:

• Thinking Kotlin requires more code
• Believing Kotlin lacks Android Studio support
• Assuming Kotlin limits programming features