Strings and Regular Expressions - The Java Programming Language - page 453

The countBetween method finds the first and last positions of the char-
acter ch in the string str . If the character does not occur twice in the
string, the method returns -1 . The difference between the two charac-
ter positions is one more than the number of characters in between (if
the two positions were 2 and 3, the number of characters in between is
zero).

Several overloads of the method indexOf search forward in a string, and
several overloads of lastIndexOf search backward. Each method returns
the index of what it found, or 1 if the search was unsuccessful:

Method Returns Index Of...

first position of ch

indexOf(int ch)

indexOf(int ch, int start) first position of ch start

first position of str

indexOf(String str)

indexOf(String str, int
start)

first position of str start

last position of ch

lastIndexOf(int ch)

lastIndexOf(int ch, int
start)

last position of ch start

last position of str

lastIndexOf(String str)