how to define comparator myself?

[lijun wang]

can I define the comarator?
for example, how can I define first>second or first<second?
String.CASE_INSENSITIVE_ORDER.compare(first, second)

Thanks!!!

[Keith Lynn]

Yes, you can create a class definition which implements the Comparator interface.

[Jeff Albertson]

Here is the source code for CASE_INSENSITIVE_ORDER, as an example:

public static final Comparator<String> CASE_INSENSITIVE_ORDER
                                         = new CaseInsensitiveComparator();
    private static class CaseInsensitiveComparator
                         implements Comparator<String>, java.io.Serializable {
        public int compare(String s1, String s2) {
            int n1=s1.length(), n2=s2.length();
            for (int i1=0, i2=0; i1<n1 && i2<n2; i1++, i2++) {
                char c1 = s1.charAt(i1);
                char c2 = s2.charAt(i2);
                if (c1 != c2) {
                    c1 = Character.toUpperCase(c1);
                    c2 = Character.toUpperCase(c2);
                    if (c1 != c2) {
                        c1 = Character.toLowerCase(c1);
                        c2 = Character.toLowerCase(c2);
                        if (c1 != c2) {
                            return c1 - c2;
                        }
                    }
                }
            }
            return n1 - n2;
        }
    }

Does anyone know why it uses both toUpperCase and toLowerCase?

[Yuriy Zilbergleyt]

Originally posted by Jeff Albertson:

Does anyone know why it uses both toUpperCase and toLowerCase?

Yeah, that does look mighty strange. I can't think of a case when (Character.toUpperCase(c1) != Character.toUpperCase(c2) && Character.toLowerCase(c1) == Character.toLowerCase(c2)) evaluates to true. Are they just being overparanoid?

Yuriy