Flow of Control - Absolute Java - page 116

PITFALL: (continued)

Notice that it is perfectly legal to use a quoted string with a String method, as in
the preceding use of equalsIgnoreCase . A quoted string is an object of type String
and has all the methods that any other object of type String has.
For the kinds of applications we are looking at in this chapter, you could also use ==
to test for equality of objects of type String , and it would deliver the correct answer.
However, there are situations in which == does not correctly test strings for equality, so
you should get in the habit of using equals rather than == to test strings. ■

Lexicographic and Alphabetical Order
The method compareTo tests two strings to determine their lexicographic order.
Lexicographic ordering is similar to alphabetic ordering and is sometimes, but not
always, the same as alphabetic ordering. The easiest way to think about lexicographic
ordering is to think of it as being the same as alphabetic ordering but with the
alphabet ordered differently . Specifically, in lexicographic ordering, the letters and other
characters are ordered as in the ASCII ordering , which is shown in Appendix 3 .
If s1 and s2 are two variables of type String that have been given String values, then

lexicographic
ordering

compareTo

s1.compareTo(s2)
returns a negative number if s1 comes before s2 in lexicographic ordering, returns zero if
the two strings are equal, and returns a positive number if s2 comes before s1 . Thus,

s1.compareTo(s2) < 0

returns true if s1 comes before s2 in lexicographic order and returns false otherwise.
For example, the following will produce correct output:

if (s1.compareTo(s2) < 0)
System.out.println(
s1 + " precedes " + s2 + " in lexicographic ordering");
else if (s1.compareTo(s2) < 0)
System.out.println(
s1 + " follows " + s2 + " in lexicographic ordering");
else //s1.compareTo(s2) == 0
System.out.println(s1 + " equals " + s2);

If you look at the ordering of characters in Appendix 3 , you will see that all
uppercase letters come before all lowercase letters. For example, 'Z' comes before 'a'
in lexicographic order. So when comparing two strings consisting of a mix of lower- and
uppercase letters, lexicographic and alphabetic ordering are not the same. However, as