str.substring(1)
creates a substring that contains all the characters from str from
character 1 to the end.
public class StringTester
{
public static int length( String str )
{
if ( str.isEmpty() )
return 0;
else
return 1 + length( str.substring(1) );
}
public static void main (String[] args)
{
String snake = "rattlesnake";
System.out.println( "Length of " + snake + " is: " + length( snake ) );
}
}
We now have all the pieces needed to complete the method.
Study how length() fits the recursive definition:
str.substring(1) is the tail of the string.length( str.substring(1) ) is the length of the tail.
Recall that in Java the index of the first character of a string is 0, so that the
str.substring(1) gives you all the characters of the string starting with
the character after the first.
However: if the string has only one character in it, then
str.substring(1) gives you an empty string.
(So the tail of a one-character string is the empty string.)
Note to AP students: the above odd fact has sometimes been needed for the free response part of the AP test.
In computing the length (11) of the example, how many objects were created by the
length() method?