Duplicated string literals make the process of refactoring error-prone, since you must be sure to update all occurrences.

On the other hand, constants can be referenced from many places, but only need to be updated in a single place.

Noncompliant Code Example

With the default threshold of 3:

class A {
    fun run() {
        prepare("string literal")    // Noncompliant - "string literal" is duplicated 3 times
        execute("string literal")
        release("string literal")
    }

    fun method() {
        println("'")                 // Compliant - literal "'" has less than 5 characters and is excluded
        println("'")
        println("'")
    }
}

Compliant Solution

class A {
    companion object {
        const val CONSTANT = "string literal"
    }

    fun run() {
        prepare(CONSTANT)    // Compliant
        execute(CONSTANT)
        release(CONSTANT)
    }
}

Exceptions

To prevent generating some false-positives, literals having 5 or less characters are excluded as well as literals containing only letters, digits and '_'.