String type and immutability in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code?

Consider the following Kotlin code snippet:

val original = "hello"
val modified = original.replace('h', 'j')
println(original)
println(modified)

What will be printed?

Kotlin

val original = "hello"
val modified = original.replace('h', 'j')
println(original)
println(modified)

A hello\njello

B hello\nhello

C jello\njello

D jello\nhello

💡 Hint

Remember that Kotlin strings are immutable. The replace function returns a new string.

The replace function does not change the original string. It returns a new string with replacements. So original remains "hello" and modified is "jello".

🧠 Conceptual

intermediate

Why are Kotlin strings immutable?

Which of the following is the main reason Kotlin strings are immutable?

A To allow strings to be changed in place without creating new objects

B To make strings mutable and faster to change

C To prevent strings from being used in collections

D To allow strings to be safely shared between threads without synchronization

💡 Hint

Think about thread safety and performance.

Immutable strings can be shared safely between threads without locks, improving performance and safety.

🔧 Debug

advanced

What error does this Kotlin code produce?

Examine this Kotlin code:

var text = "hello"
text[0] = 'j'
println(text)

What error will this code cause?

Kotlin

var text = "hello"
text[0] = 'j'
println(text)

A Error: Val cannot be reassigned

B Error: Unresolved reference to 'text'

C Error: String cannot be assigned to by index

D No error, prints 'jello'

💡 Hint

Think about whether Kotlin strings allow changing characters by index.

Kotlin strings are immutable. You cannot assign a character to a specific index. This causes a compilation error.

🚀 Application

advanced

How to create a new string with a changed first character?

You want to change the first character of a Kotlin string str to 'J'. Which code snippet correctly does this?

A val newStr = "J" + str.substring(1)

B str[0] = 'J'; val newStr = str

C val newStr = str.replaceAt(0, 'J')

D val newStr = str.setCharAt(0, 'J')

💡 Hint

Remember strings are immutable, so you must create a new string.

Concatenating 'J' with the substring from index 1 creates a new string with the first character changed.

❓ Predict Output

expert

What is the output of this Kotlin code involving string references?

Consider this Kotlin code:

val a = "test"
val b = a
val c = b.replace('t', 'b')
println(a)
println(b)
println(c)

What will be printed?

Kotlin

val a = "test"
val b = a
val c = b.replace('t', 'b')
println(a)
println(b)
println(c)

A best\nbest\nbesb

B test\ntest\nbesb

C test\ntest\ntest

D test\nbest\nbesb

💡 Hint

Remember that b is just a reference to a, and strings are immutable.

Both a and b refer to the same string "test". The replace creates a new string c with replacements. So a and b print "test", c prints "besb".