String methods (substring, split, trim) in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the substring "Hello" from the string.

Kotlin

val text = "Hello, World!"
val sub = text.[1](0, 5)
println(sub)

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

Asubstring

Bsplit

Ctrim

Dreplace

Attempts:

3 left

💡 Hint

Common Mistakes

Using split instead of substring will not extract a substring by index.

Using trim removes spaces but does not extract parts of the string.

The substring method extracts a part of the string from index 0 to 5 (exclusive), giving "Hello".

2fill in blank

medium

Complete the code to split the string into words using space as separator.

Kotlin

val sentence = "Kotlin is fun"
val words = sentence.[1](" ")
println(words.joinToString(", "))

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

Atrim

Bsplit

Csubstring

Dreplace

Attempts:

3 left

💡 Hint

Common Mistakes

Using substring will not split the string into parts.

Using trim only removes spaces at the ends, not inside the string.

The split method divides the string into parts using the space character, resulting in a list of words.

3fill in blank

hard

Fix the error in the code to remove spaces from the start and end of the string.

Kotlin

val raw = "  Kotlin  "
val clean = raw.[1]()
println("'$clean'")

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

Atrim

Bsplit

Csubstring

Dreplace

Attempts:

3 left

💡 Hint

Common Mistakes

Using split will not remove spaces but split the string.

Using substring requires indexes and does not remove spaces automatically.

The trim method removes spaces from the start and end of the string, cleaning it up.

4fill in blank

hard

Fill both blanks to get the last word from the sentence.

Kotlin

val sentence = "Learn Kotlin easily"
val words = sentence.[1](" ")
val lastWord = words[[2]]
println(lastWord)

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

Asplit

Btrim

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using trim instead of split will not create a list of words.

Using index 0 will give the first word, not the last.

First, split divides the sentence into words. Then, index 2 accesses the last word "easily".

5fill in blank

hard

Fill all three blanks to extract "Kotlin" from the string with spaces.

Kotlin

val raw = "  Learn Kotlin  "
val clean = raw.[1]()
val words = clean.[2](" ")
val word = words[[3]]
println(word)

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

Atrim

Bsplit

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Not trimming first leaves spaces in the words.

Using index 0 selects "Learn", not "Kotlin".

First, trim removes spaces around the string. Then, split breaks it into words. Finally, index 1 selects "Kotlin".

Practice

1. What does the Kotlin trim() method do when called on a string?

easy

A. Converts the string to uppercase

B. Splits the string into parts based on spaces

C. Extracts a part of the string by index

D. Removes spaces from the start and end of the string

Solution

1. Step 1: Understand the purpose of trim()

   The trim() method removes whitespace characters from the beginning and end of a string.

2. Step 2: Compare with other string methods

   Unlike split() or substring(), trim() does not split or extract parts but cleans spaces around the string.

3. Final Answer:

   Removes spaces from the start and end of the string -> Option D

4. Quick Check:

   trim() removes outer spaces [OK]

Hint: trim() cleans spaces only at string edges [OK]

Common Mistakes:

• Thinking trim() splits the string
• Confusing trim() with substring()
• Assuming trim() changes case

2. Which of the following is the correct Kotlin syntax to get a substring from index 2 to 5 (exclusive) of a string text?

easy

A. text.substring(2..5)

B. text.subString(2, 5)

C. text.substring(2, 5)

D. text.substring(2, 6)

Solution

1. Step 1: Recall Kotlin substring syntax

   The correct method call is substring(startIndex, endIndex) where endIndex is exclusive.

2. Step 2: Check each option

   text.substring(2..5) uses a range which is invalid for substring. text.subString(2, 5) has wrong capitalization. text.substring(2, 6) uses 6 as endIndex which extracts more characters than asked.

3. Final Answer:

   text.substring(2, 5) -> Option C

4. Quick Check:

   substring(start, end) uses exclusive end [OK]

Hint: Use substring(start, end) with end exclusive [OK]

Common Mistakes:

• Using range syntax inside substring
• Wrong method name capitalization
• Confusing inclusive vs exclusive end index

3. What is the output of the following Kotlin code?

val data = " apple, banana , cherry "
val fruits = data.trim().split(",")
println(fruits[1].trim())

medium

A. ananab

B. banana

C. anana

D. banan

Solution

1. Step 1: Apply trim() on the original string

   Calling trim() removes spaces at start and end, so string becomes "apple, banana , cherry".

2. Step 2: Split by comma and trim the second element

   Splitting by "," gives ["apple", " banana ", " cherry"]. Then trimming the second element " banana " removes spaces, resulting in "banana".

3. Final Answer:

   banana -> Option B

4. Quick Check:

   trim() cleans spaces after split [OK]

Hint: Trim after split to remove spaces around parts [OK]

Common Mistakes:

• Not trimming after split, leaving spaces
• Assuming split trims automatically
• Confusing index positions in list

4. Find the error in this Kotlin code snippet:

val sentence = "Hello World"
val part = sentence.substring(6, 5)
println(part)

medium

A. substring end index is less than start index causing error

B. substring method requires only one argument

C. substring indexes are inclusive, so 6 to 5 is valid

D. No error, output is "World"

Solution

1. Step 1: Check substring parameters

   substring(startIndex, endIndex) requires startIndex ≤ endIndex. Here, startIndex=6 and endIndex=5, which is invalid.

2. Step 2: Understand Kotlin substring behavior

   This causes an exception because the end index is less than the start index.

3. Final Answer:

   substring end index is less than start index causing error -> Option A

4. Quick Check:

   substring end must be ≥ start [OK]

Hint: End index must be >= start index in substring [OK]

Common Mistakes:

• Assuming substring indexes are inclusive
• Using end index less than start index
• Thinking substring accepts one argument only

5. Given a string input = " red, green , blue , yellow ", write Kotlin code to create a list of trimmed color names without spaces. Which code snippet correctly achieves this?

hard

A. input.split(",").map { it.trim() }

B. input.trim().split(",")

C. input.split(",").trim()

D. input.trim().map { it.split(",") }

Solution

1. Step 1: Split the string by commas

   Using split(",") breaks the string into parts including spaces.

2. Step 2: Trim spaces from each part

   Using map { it.trim() } removes spaces from each color name, producing a clean list.

3. Step 3: Evaluate other options

   input.trim().split(",") trims only the ends before splitting, so inner spaces remain. input.split(",").trim() tries to trim a list, which is invalid. input.trim().map { it.split(",") } trims the whole string then maps incorrectly.

4. Final Answer:

   input.split(",").map { it.trim() } -> Option A

5. Quick Check:

   Split then trim each part for clean list [OK]

Hint: Split first, then trim each piece with map [OK]

Common Mistakes:

• Trimming before split only removes outer spaces
• Trying to trim a list directly
• Incorrect chaining of methods