Kotlin Equivalent of Java’s equalsIgnoreCase()

1. Introduction

String comparison is an essential aspect of programming. Java’s equalsIgnoreCase() method is a popular choice for case-insensitive comparison of string objects. However, in Kotlin, there are various ways to achieve the same functionality.

This tutorial explores some of the best practices for achieving case-insensitive string comparison in Kotlin.

2. Using the equals() Method and the ignoreCase Parameter

One of the simplest ways to achieve case-insensitive string comparison in Kotlin is by using the equals() method and overriding the default for the ignoreCase parameter and passing true. This allows the equals() method to perform the comparison between two strings without considering their case differences:

@Test
fun `test string case insensitive comparison using equals methods`() {
    val result1 = "Hello".equals("hello", true)
    val result2 = "Hello".equals("world", true)

    assertTrue(result1)
    assertFalse(result2)
}

In this code snippet, we check the equality of two strings with the version of equals() that accepts the ignoreCase parameter. By setting the ignoreCase parameter to true, it will return true if both strings are equal, regardless of any case differences.

From this test, we observe that the strings “Hello” and “hello” are equal if we don’t consider the case difference between them. Likewise, the strings “Hello” and “world” are not equal even if the cases are ignored.

3. Using the equals() and lowercase() Methods

Another interesting approach to achieving case-insensitive string comparison in Kotlin is by using the equals() method along with the lowercase() method. The lowercase() method converts the string to lowercase, allowing us to handle any case differences when comparing with another string:

@Test
fun `test string case insensitive comparison using equals and lowercase methods`() {
    val result1 = "Hello".lowercase() == "hello".lowercase()
    val result2 = "Hello".lowercase() == "world".lowercase()

    assertTrue(result1)
    assertFalse(result2)
}

In the unit test above, we convert two strings to lowercase using the lowercase() method. We use equals() as an operator function to check if the lowercase strings are equal or not. Note that, the equals() method is usually preferred because it handles null safety directly and is simple to use. However, we can only use the operator function when we don’t need to pass a value for the ignoreCase parameter

The first assert statement returns true for the strings “Hello” and “hello”. The second statement returns false because the strings “Hello” and “world” are not the same even after converting them to their lowercase equivalents.

4. Using the compareTo() Method

Finally, we can handle case-insensitive comparisons in Kotlin using the compareTo() method of the String class. This method compares two strings and returns a value indicating whether one string is less than, equal to, or greater than the other string. This method also has an optional ignoreCase parameter that we can set to true to ignore case differences:

@Test
fun `test string case insensitive comparison using compareTo method`() {
    val result1 = "Hello".compareTo("hello", true) == 0
    val result2 = "Hello".compareTo("world", true) == 0

    assertTrue(result1)
    assertFalse(result2)
}

In the code snippet above, we use the compareTo() method to check if two strings are equal, ignoring the case differences. If the strings are equal, the compareTo() method will return zero.

Next, we assert that the strings “Hello” and “hello” are equal with this strategy. Likewise, we can also assert that the strings “Hello” and “world” aren’t equal.

5. Conclusion

In this article, we’ve explored various ways to achieve Java’s equalsIgnoreCase() method in Kotlin. All the approaches we’ve discussed involve the use of Kotlin’s built-in methods. Choosing the right method depends on the project’s specific use case and personal preference.