source-code about String.comareTo method.

here is part of the 'compareToIgnoreCase' method:
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; } } }
what confused me was that,why it needs to be converted to 'LowerCase' after converted to 'UpperCase'? I mean either of the two will be ok....

No, it isn't enough to compare the original characters followed by their upper-cased versions. If the two characters being compared are İ (the Turkish uppercase dotted i) and ı (the Turkish lowercase dotless i) then you need to convert them both to uppercase (yielding İ and I) and then back to lowercase (yielding i and i) before you know they are the same except for case. Provided your default locale isn't Turkish, that is.

Have a look at this article for more about those letters: Dotted and dotless I.

Paul Clapham wrote:No, it isn't enough to compare the original characters followed by their upper-cased versions. If the two characters being compared are İ (the Turkish uppercase dotted i) and ı (the Turkish lowercase dotless i) then you need to convert them both to uppercase (yielding İ and I) and then back to lowercase (yielding i and i) before you know they are the same except for case. Provided your default locale isn't Turkish, that is.

Have a look at this article for more about those letters: Dotted and dotless I.

got it,thanks very much for your response...