Platform types from Java interop in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely call a Java method that returns a platform type.

Kotlin

val length = javaString?.[1]

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

Alength

Blength()

Csize

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using length without parentheses causes an error.

Java strings use length() method, so you must call it with parentheses.

2fill in blank

medium

Complete the code to safely handle a platform type that might be null.

Kotlin

val safeString: String = javaString[1] ?: "default"

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

A?.

B?

C!!

D?:

Attempts:

3 left

💡 Hint

Common Mistakes

Using ? or ?. does not assert non-null.

The !! operator asserts the value is not null, throwing an exception if it is.

3fill in blank

hard

Fix the error in calling a Java method returning a platform type that might be null.

Kotlin

val length = javaString.[1]

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

Alength()!!

Blength()

Clength

Dlength!!

Attempts:

3 left

💡 Hint

Common Mistakes

Using length property causes error.

Forgetting !! leads to nullable type.

Calling length() and then asserting non-null with !! ensures safe usage.

4fill in blank

hard

Fill both blanks to safely check and use a platform type from Java.

Kotlin

if (javaString [1] null) {
    val length = javaString.[2]()
}

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

A!=

B==

Clength

Attempts:

3 left

💡 Hint

Common Mistakes

Using == null instead of != null.

Using property length instead of method length().

Check if javaString is not null, then call length() method.

5fill in blank

hard

Fill all three blanks to create a safe call chain with platform types from Java.

Kotlin

val length = javaString[1]?.[2]()?.let { it [3] 0 } ?: -1

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

A!!

Blength

C>

Attempts:

3 left

💡 Hint

Common Mistakes

Using property length without parentheses.

Missing null assertion operator.

Assert non-null with !!, call length(), then check if length is greater than zero.