Kotlin string class and its methods

A string variable is an object of type String, and since an object in Kotlin has a number of methods and properties, a String object is itself equipped with a lot of methods to perform many operations, such as calculating the length of a string, testing whether or not a string contains a character or a substring, extracting a substring ... Here is a collection of these methods:

char charAt (int index)
Returns the character that is at index. (The first character is at index 0.)
This method returns an exception of type IndexOutOfBoundsException.
int compareTo (String string_to_comparer)
Compare two String alphabetically.
int compareToIgnoreCase (String String)
Compares two String alphabetically, ignoring the case.
boolean contains (chars)
Returns true only if the String contains the same sequence of characters.
This method returns an exception of type NullPointerException.
boolean startsWith (String prefix)
Returns true if the String starts with prefix.
boolean endsWith (String suffix)
Returns true if the String ends with suffix.
boolean equals (Object other_obj)
Compare the String with other_obj.
indexOf int (int ch [, int index])
Returns the index of the first occurrence of the ch character.
If index is indicated, the search starts from this index.
indexOf int (String s [, int index])
Returns the index of the first occurrence of the String s.
If index is indicated, the search starts from this index.
int lastIndexOf (int ch [, int fromIndex])
Returns the index of the last occurrence of the character ch.
If index is indicated, the search starts from this index.
int lastIndexOf (String str [, int fromIndex])
Returns the index of the last occurrence of the String s.
If fromIndex is specified, the search starts from this index.
int length ()
Returns the size of the String.
boolean isEmpty ()
Returns true if the size of the String is 0.
boolean matches (String regex)
Returns true if the String matches the regex regular expression.
This method returns an exception of type PatternSyntaxException.
String concat (String string)
Concatenate the String string at the end of the String that calls the method.
String replace (old tank, new tank)
Replaces all occurrences of old with new, then returns the modified string.
String replaceAll (String regex, String new)
Replaces all occurrences matching the regex regular expression with new, then returns the modified string.
This method returns an exception of type PatternSyntaxException.
String replaceFirst (String regex, String new)
Replaces the first occurrence corresponding to the regex regular expression with new, then returns the modified string.
This method returns an exception of type PatternSyntaxException.
String [] split (String regex)
Cut the String using the regex regular expression.
This method returns an exception of type PatternSyntaxException.
String substring (int start)
Returns a new String that contains characters from the beginning to the end of the String.
This method returns an exception of type IndexOutOfBoundsException.
String substring (int start, int end)
Returns a new String that contains characters from beginning to end.
This method returns an exception of type IndexOutOfBoundsException.
String toLowerCase ()
Converts all characters to lowercase.
String toUpperCase ()
Converts all characters to uppercase.
String trim ()
Returns the String without spaces at the beginning and end.

Example1

fun main(args: Array< string>) {
  var b = "hello"
  var b1 = b.substring(0,3)
    println(b1)
  // This example extracts from the string b a substring b1 = "hel"
}

Example 2

import java.util.*
fun main(args: Array< string>) {
  var s1= "auto"
  var s2 = s1.toUpperCase()
  println(s2)
  //this example will show the string in upper case: AUTO
}