Why is this an issue?
In Kotlin, == means structural equality and != structural inequality and both map to the left-side term’s
equals() function. It is, therefore, redundant to call equals() as a function. Also, == and != are
more general than equals() and !equals() because it allows either of both operands to be null.
Developers using equals() instead of == or != is often the result of adapting styles from other languages
like Java, where == means reference equality and != means reference inequality.
What is the potential impact?
Wrong logic
== and != allow either of both operands to be null, while equals() doesn’t.
Readability and Understanding
The == and != operators are a more concise and elegant way to test structural equality than calling a function.
How to fix it
Replace a.equals(b) with a == b. Replace !a.equals(b) with a != b.
Code examples
Noncompliant code example
data class Person(
val name: String,
val firstName: String,
val age: Int,
val address: String
)
fun checkEquality() {
val personA = Person("Claus", "Santa", 200, "North Pole")
val personB = Person("Nicholas", "Saint", 1700, "Myra")
if (personA.name.equals(personB.name)) { // Noncompliant, should use `==` instead
// ...
}
if (!personA.equals(personB)) { // Noncompliant, should use `!=` instead
// ...
}
}
Compliant solution
fun checkEquality() {
val personA = Person("Claus", "Santa", 200, "North Pole")
val personB = Person("Nicholas", "Saint", 1700, "Myra")
if (personA.name == personB.name) { // Compliant
// ...
}
if (personA != personB) { // Compliant
// ...
}
}
Resources
Documentation
