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Summary - Advanced strings

Combine Regex, StringBuilder and trim to write a CSV parser.

Summary - Advanced strings

In this group you learned regular expressions, matching with matches and find, transforming with replace, efficient joining with StringBuilder and edge shaping with trim/padStart.

Now it is time to combine them in a single task: find the digits in a text, trim the spaces and print the result. This is a small sample of a real text-processing pipeline.

Practice Clean text and replace digits

First trim the string " a1b22 " to remove edge spaces. Then replace the digits with Regex("\\d+") using "#" and print.

Starter code

Main.kt
fun main() {
    val r = Regex("\\d+")
    // First trim, then replace digits with diyez, print
}

Sample solution

Main.kt
val r = Regex("\\d+")
println("  a1b22  ".trim().replace(r, "#"))

Expected output

a#b#

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match tool to purpose

Term Meaning
Regex Pattern match
find First match
replace Substitute
trim Edge cleanup

2 Fill in the blank: builder to string

Question 
val sb = StringBuilder("hi")
val s = sb.____()
Answer 
val sb = StringBuilder("hi")
val s = sb.toString()

Explanation: toString returns the builder's content as a string.

3 You concatenate 500 times in a loop. Which is best?

  • StringBuilder Correct answer
  • Regex
  • String +
  • trim

Explanation: Is StringBuilder; it does not create a new object per append.

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together