How Kotlin compiles to JVM bytecode - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

Kotlin

fun greet() : String = [1]

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

Aprintln("Hello, JVM!")

B"Hello, JVM!"

CHello, JVM!

Dreturn "Hello, JVM!"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string

Using println instead of returning a string

The function returns the string "Hello, JVM!". It must be a string literal.

2fill in blank

medium

Complete the code to create a Kotlin class with a primary constructor that takes a name.

Kotlin

class Person(val [1]: String)

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

Aname

Btitle

Cid

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated parameter names like age or id

Forgetting to declare the parameter as val or var

The primary constructor parameter is named name to represent a person's name.

3fill in blank

hard

Fix the error in the Kotlin function that prints a message.

Kotlin

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

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

AHello JVM

Bprintln("Hello JVM")

C"Hello JVM"

Dreturn "Hello JVM"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing unquoted text causing syntax errors

Using return inside println

The argument to println must be a string literal, so it needs quotes.

4fill in blank

hard

Fill both blanks to create a Kotlin map comprehension that filters entries with values greater than 10.

Kotlin

val filtered = mapOf(1 to 5, 2 to 15, 3 to 20).filter { it.[1] [2] 10 }

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

Avalue

B>

C<

Dkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using key instead of value

Using less than operator instead of greater than

The filter checks if the value of each entry is greater than 10.

5fill in blank

hard

Fill all three blanks to create a Kotlin map from a list of words with their lengths, filtering words longer than 3 letters.

Kotlin

val words = listOf("cat", "house", "dog", "elephant")
val lengths = words.associateWith { it.[1] }
val filtered = lengths.filter { it.key.[2] [3] 3 }

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

Alength

C>

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using count which is a function, not a property

Using key incorrectly in associateWith

The associateWith uses it.length to get word lengths. The filter checks if the word length is greater than 3.

Practice

1. What does Kotlin compile into so it can run on the Java Virtual Machine?

easy

A. Kotlin script

B. Java source code

C. Machine code

D. JVM bytecode

Solution

1. Step 1: Understand Kotlin compilation target

   Kotlin code is compiled into a form that the Java Virtual Machine (JVM) can understand.

2. Step 2: Identify the JVM compatible format

   The JVM runs bytecode, which is a low-level, platform-independent code format.

3. Final Answer:

   JVM bytecode -> Option D

4. Quick Check:

   Kotlin compiles to JVM bytecode [OK]

Hint: Kotlin runs on JVM by compiling to JVM bytecode [OK]

Common Mistakes:

• Thinking Kotlin compiles directly to machine code
• Confusing Kotlin source with Java source
• Assuming Kotlin scripts run without compilation

2. Which command is used to compile Kotlin code into JVM bytecode?

easy

A. java

B. kotlinc

C. javac

D. kotlin

Solution

1. Step 1: Identify Kotlin compiler command

   The Kotlin compiler command is used to convert Kotlin source code into JVM bytecode.

2. Step 2: Match the correct command

   The official Kotlin compiler command is kotlinc, not java or javac.

3. Final Answer:

   kotlinc -> Option B

4. Quick Check:

   Kotlin compiler command = kotlinc [OK]

Hint: Remember Kotlin compiler command is kotlinc, not javac [OK]

Common Mistakes:

• Using 'java' instead of 'kotlinc' to compile
• Confusing 'javac' (Java compiler) with Kotlin compiler
• Using 'kotlin' instead of 'kotlinc'

3. What will be the output when running Kotlin code compiled to JVM bytecode on a Java Virtual Machine?

medium

A. It runs on any JVM supporting the bytecode version

B. It runs only on Kotlin-specific virtual machines

C. It runs only on Android devices

D. It runs only on Windows OS

Solution

1. Step 1: Understand JVM bytecode portability

   JVM bytecode is platform-independent and runs on any JVM implementation that supports the bytecode version.

2. Step 2: Identify supported platforms

   Since JVM runs on many OSes and devices, Kotlin bytecode runs anywhere JVM runs.

3. Final Answer:

   It runs on any JVM supporting the bytecode version -> Option A

4. Quick Check:

   Kotlin bytecode runs on any JVM [OK]

Hint: JVM bytecode runs anywhere JVM runs, not limited to OS [OK]

Common Mistakes:

• Thinking Kotlin bytecode runs only on Android
• Assuming it needs a Kotlin-specific VM
• Believing it runs only on Windows

4. You wrote Kotlin code and compiled it with kotlinc, but running java MyProgram gives an error. What is the likely cause?

medium

A. You forgot to specify the main class in the command

B. Kotlin code cannot be run on JVM

C. You used the wrong Kotlin compiler

D. The JVM does not support Kotlin bytecode

Solution

1. Step 1: Understand running Kotlin bytecode on JVM

   After compiling, you must specify the main class name when running with java.

2. Step 2: Identify common mistake

   Running java MyProgram without the correct class or classpath causes errors.

3. Final Answer:

   You forgot to specify the main class in the command -> Option A

4. Quick Check:

   Run java with main class specified [OK]

Hint: Always specify main class when running with java command [OK]

Common Mistakes:

• Assuming Kotlin code can't run on JVM
• Using wrong compiler command
• Believing JVM lacks Kotlin support

5. You want to create a Kotlin program that runs on JVM and Android. How does compiling to JVM bytecode help achieve this?

hard

A. JVM bytecode only runs on desktop JVMs

B. JVM bytecode runs natively on Android without changes

C. JVM bytecode can be converted to Android's Dalvik bytecode easily

D. Kotlin code must be rewritten for Android

Solution

1. Step 1: Understand Kotlin compilation targets

   Kotlin compiles to JVM bytecode which runs on JVM, and can be converted to Dalvik bytecode for Android.

2. Step 2: Recognize Android bytecode conversion

   Android uses Dalvik/ART runtime, which requires converting JVM bytecode to its format.

3. Final Answer:

   JVM bytecode can be converted to Android's Dalvik bytecode easily -> Option C

4. Quick Check:

   Kotlin JVM bytecode converts to Android bytecode [OK]

Hint: JVM bytecode converts to Android bytecode for cross-platform [OK]

Common Mistakes:

• Thinking JVM bytecode runs unchanged on Android
• Believing Kotlin must be rewritten for Android
• Assuming JVM bytecode only runs on desktops