Check if a string contains only letters - kotlin

Question

How I can make a function that take a string and return the result whether the string contain alphabet letter only or not.

Answer 1

function all returns true if all characters match the given predicate.
fun String.onlyLetters() = all { it.isLetter() }
if (str.onlyLetters()) {
// only letters
}
else {
}

Answer 2

You can use the function firstOrNull() to search for the 1st non letter char and compare the result with null:
fun onlyLetters(s: String): Boolean = (s.firstOrNull { !it.isLetter() } == null)
or as an extension function:
fun String.onlyLetters(): Boolean = (firstOrNull { !it.isLetter() } == null)
Note that this way you will get true even if the string is empty.
If you don't want this then you should add another condition for the length like:
fun String.onlyLetters(): Boolean = length > 0 && (firstOrNull { !it.isLetter() } == null)

Answer 3

You could use a simple regular expression to validate the input:
fun isOnlyLetters(word: String): Boolean {
val regex = "^[A-Za-z]*$".toRegex()
return regex.matches(word)}
Alternatively,
making the regex ^[A-Za-z ]*$ (space after "z")would allow any amount of whitespace (such as in a phrase) at any point in the string (i.e. and still return true).
making the regex ^[A-Za-z ]+$ (* -> +) would return false for an empty string(i.e. ensure that there is at least one character in the input, be it a letter or space).

Answer 4

create an extension function isLettersOnly()
/*
* This fuction return true only if the string contain a-z or A-Z,
* Otherwise false*/
fun String.isLettersOnly(): Boolean {
val len = this.length
for (i in 0 until len) {
if (!this[i].isLetter()) {
return false
}
}
return true
}
1.check a string value
fun main() {
val text = "name"
if (text.isLettersOnly()) {
println("This is contain a-z,A-Z only")
} else {
println("This contain something else")
}
}
output:
This is contain a-z,A-Z only
2.check a string value
fun main() {
val text = "name 5"
if (text.isLettersOnly()) {
println("This is contain a-z,A-Z only")
} else {
println("This contain something else")
}
}
output:
This contain something else