Flow of Control - Java - page 110

PITFALL: (continued)

The method equalsIgnoreCase behaves similarly to equals , except that with
equalsIgnoreCase , the upper- and lowercase versions of the same letter are considered
the same. For example, "Hello" and "hello" are not equal because their first characters,
'H' and 'h' , are different characters. But they would be considered equal by the method
equalsIgnoreCase . For example, the following will output Equal ignoring case. :

if ("Hello".equalsIgnoreCase("hello"))
System.out.println("Equal ignoring case.");

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. Lexi-
cographic 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);