String methods (substring, split, trim) in Kotlin - Mini Project: Build & Apply

Working with String Methods in Kotlin

📖 Scenario: You are helping a small bookstore organize customer feedback. The feedback comes as a long string with customer names and their comments separated by commas. You want to clean and split this data to make it easier to read and analyze.

🎯 Goal: Build a Kotlin program that trims extra spaces from the feedback string, splits it into individual feedback entries, and extracts the customer names using substring.

📋 What You'll Learn

Create a string variable with the exact feedback text

Create a variable to hold the trimmed version of the feedback string

Split the trimmed string into a list of feedback entries

Extract customer names from each feedback entry using substring

Print the list of customer names

💡 Why This Matters

🌍 Real World

Cleaning and organizing customer feedback or any text data is common in businesses to understand opinions and improve services.

💼 Career

Knowing how to manipulate strings is essential for software developers, data analysts, and anyone working with text processing or user input.

1

Create the feedback string

Create a string variable called feedback with this exact value: " Alice: Loved the new books, Bob: Great service, Charlie: Will visit again "

Kotlin

# Create the feedback string variable called feedback
# Your code here

Hint

Use val feedback = "your string here" to create the string.

2

Trim the feedback string

Create a variable called trimmedFeedback that holds the result of trimming spaces from feedback using the trim() method

Kotlin

val feedback = "  Alice: Loved the new books, Bob: Great service, Charlie: Will visit again  "
# Trim the feedback string and store in trimmedFeedback
# Your code here

Hint

Use val trimmedFeedback = feedback.trim() to remove spaces at the start and end.

3

Split the trimmed feedback into entries

Create a variable called entries that splits trimmedFeedback by comma and space ", " using the split() method

Kotlin

val feedback = "  Alice: Loved the new books, Bob: Great service, Charlie: Will visit again  "
val trimmedFeedback = feedback.trim()
# Split trimmedFeedback into entries by ", "
# Your code here

Hint

Use val entries = trimmedFeedback.split(", ") to split the string into parts.

4

Extract and print customer names

Create a list called names by extracting the substring before the colon ':' from each entry in entries. Then print names. Use a for loop with variable entry and the substringBefore method.

Kotlin

val feedback = "  Alice: Loved the new books, Bob: Great service, Charlie: Will visit again  "
val trimmedFeedback = feedback.trim()
val entries = trimmedFeedback.split(", ")
# Extract names from entries and print the list
# Your code here

Hint

Use entry.substringBefore(':') inside a loop to get each name, then print the list.

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