Why Java interop matters in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Java ArrayList in Kotlin.

Kotlin

val list = [1]<String>()

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AList

BArrayList

CMutableList

DSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using Kotlin's List which is immutable by default.

Using Set which is a different collection type.

In Kotlin, to create a Java ArrayList, you use ArrayList which is interoperable with Java's ArrayList.

2fill in blank

medium

Complete the code to call a Java method from Kotlin.

Kotlin

val result = javaObject.[1]()

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AtoString

Binvoke

CjavaMethod

Dcall

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that don't exist on the Java object.

Trying to call Kotlin-specific functions on Java objects.

The toString() method is a common Java method that can be called from Kotlin on any Java object.

3fill in blank

hard

Fix the error in calling a Java static method from Kotlin.

Kotlin

val max = Math.[1](5, 10)

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AmaxValue

Bmaximum

CmaxOf

Dmax

Attempts:

3 left

💡 Hint

Common Mistakes

Using Kotlin's maxOf instead of Java's Math.max.

Using incorrect method names that don't exist.

The Java Math class has a static method called max to get the maximum of two numbers.

4fill in blank

hard

Fill both blanks to create a Java HashMap and add an entry in Kotlin.

Kotlin

val map = [1]<String, Int>()
map.[2]("key", 1)

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AHashMap

Bput

Cadd

DMutableMap

Attempts:

3 left

💡 Hint

Common Mistakes

Using Kotlin's MutableMap instead of Java's HashMap.

Using add instead of put to add entries.

Java's HashMap is used to create the map, and put adds a key-value pair.

5fill in blank

hard

Fill all three blanks to iterate over a Java ArrayList in Kotlin and print each item.

Kotlin

val list = [1]<String>()
list.add("apple")
for ([2] in list) {
    println([3])
}

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

AArrayList

Bitem

DMutableList

Attempts:

3 left

💡 Hint

Common Mistakes

Using Kotlin's MutableList instead of Java's ArrayList.

Using different variable names inconsistently.

We create a Java ArrayList, use item as the loop variable, and print item.