Strings and Regular Expressions - The Java Programming Language - page 452

Constructs a new String with the same contents as the given
StringBuffer .
The most basic methods of String objects are length and charAt , as
defined by the CharSequence interface. This loop counts the number of
each kind of character in a string:
for (int i = 0; i < str.length(); i++)
counts[str.charAt(i)]++;
Note that length is a method for String , while for array it is a fieldit's
common for beginners to confuse the two.
In most String methods, a string index position less than zero or greater
than length()-1 throws an IndexOutOfBoundsException . Some implementa-
tions throw the more specific StringIndexOutOfBoundsException , which can
take the illegal index as a constructor argument and then include it in a
detailed message. Methods or constructors that copy values to or from
an array will also throw IndexOutOfBoundsException if any attempt is made
to access outside the bounds of that array.
There are also simple methods to find the first or last occurrence of a
particular character or substring in a string. The following method re-
turns the number of characters between the first and last occurrences
of a given character in a string:
static int countBetween(String str, char ch) {
int begPos = str.indexOf(ch);
if (begPos < 0) // not there
return -1;
int endPos = str.lastIndexOf(ch);
return endPos - begPos - 1;
}