jshell> String s = "abcdefghijklmnopq";
s ==> "abcdefghijklmnopq"

jshell> s.charAt(5);
$2 ==> 'f'

jshell> s.charAt(10);
$3 ==> 'k'

jshell> s.charAt(100);
|  Exception java.lang.StringIndexOutOfBoundsException: String index out of range: 100
|        at StringLatin1.charAt (StringLatin1.java:48)
|        at String.charAt (String.java:712)
|        at (#4:1)

jshell> "cde"
$5 ==> "cde"

jshell> s.substring(2,5)
$6 ==> "cde"

jshell> s.sub
subSequence(   substring(     
jshell> s.subring(2)
|  Error:
|  cannot find symbol
|    symbol:   method subring(int)
|  s.subring(2)
|  ^-------^

jshell> s.substring(2)
$7 ==> "cdefghijklmnopq"

jshell> s.indexOf("k")
$8 ==> 10

jshell> s.indexOf('k')
$9 ==> 10

jshell> s.indexOf('k', 12)
$10 ==> -1

jshell> s.isEmpty()
$11 ==> false

jshell>