Posted in kotlin

Comparing two strings in Kotlin – Multiple ways with real example

   October 25, 2023
Kotlin @ Freshers.in

In Kotlin, comparing two strings can be achieved in multiple ways. Depending on the nature of the comparison, you can decide to use one approach over another. Here, we’ll explore the most common methods for string comparison in Kotlin:

  1. Using == and != Operators: This checks for structural equality.
  2. Using the equals() Method: This also checks for structural equality, but with an option to ignore case.
  3. Using compareTo() Method: For lexicographical comparison.

1. Using == and != Operators

In Kotlin, the == operator checks for structural equality of two strings, i.e., it checks if the content of the two strings is the same. This is unlike Java, where == checks for reference equality.

val str1 = "Hello"
val str2 = "Hello"
val str3 = "World"

println(str1 == str2)  // true
println(str1 == str3)  // false

2. Using the equals() Method

The equals() method is another way to compare the content of two strings. The advantage here is that you can also specify if the comparison should be case-sensitive.

val str1 = "Hello"
val str2 = "HELLO"
println(str1.equals(str2))           // false
println(str1.equals(str2, true))     // true

3. Using compareTo() Method

The compareTo() method provides a way to do lexicographical comparison. It returns 0 if the strings are equal, a negative number if the first string comes before the second, and a positive number otherwise. Like equals(), you can also specify if the comparison should be case-sensitive.

val str1 = "apple"
val str2 = "banana"
val str3 = "apple"
println(str1.compareTo(str2))       // negative value
println(str1.compareTo(str3))       // 0
println(str1.compareTo(str2, true)) // negative value

Example

Here’s a simple program that you can run in any online Kotlin compiler:

fun main() {
    val strA = "Kotlin"
    val strB = "kOTLIN"
    val strC = "Java"
    // Using `==` operator
    println("Using `==` operator:")
    println("strA == strB: ${strA == strB}")
    println("strA == strC: ${strA == strC}")
    // Using `equals()` method
    println("\nUsing `equals()` method:")
    println("strA.equals(strB): ${strA.equals(strB)}")
    println("strA.equals(strB, true): ${strA.equals(strB, true)}")
    // Using `compareTo()` method
    println("\nUsing `compareTo()` method:")
    println("strA.compareTo(strB): ${strA.compareTo(strB)}")
    println("strA.compareTo(strB, true): ${strA.compareTo(strB, true)}")
    println("strA.compareTo(strC): ${strA.compareTo(strC)}")
}
Output
Using `==` operator:
strA == strB: false
strA == strC: false

Using `equals()` method:
strA.equals(strB): false
strA.equals(strB, true): true

Using `compareTo()` method:
strA.compareTo(strB): -32
strA.compareTo(strB, true): 0
strA.compareTo(strC): 1
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