Java String類中CaseInsensitiveComparator.compare()方法的實現

標籤：

String對象的大小寫不敏感比較方法的實現如下：

 1         public int compare(String s1, String s2) { 2             int n1 = s1.length(); 3             int n2 = s2.length(); 4             int min = Math.min(n1, n2); 5             for (int i = 0; i < min; i++) { 6                 char c1 = s1.charAt(i); 7                 char c2 = s2.charAt(i); 8                 if (c1 != c2) { 9                     c1 = Character.toUpperCase(c1);10                     c2 = Character.toUpperCase(c2);11                     if (c1 != c2) {12                         c1 = Character.toLowerCase(c1);13                         c2 = Character.toLowerCase(c2);14                         if (c1 != c2) {15                             // No overflow because of numeric promotion16                             return c1 - c2;17                         }18                     }19                 }20             }21             return n1 - n2;22         }

這裡，同時比較了UpperCase和LowerCase，是為了相容Georgian字元。

見String類的regionMatches()方法。如下(29~32行)：

 1     public boolean regionMatches(boolean ignoreCase, int toffset, 2             String other, int ooffset, int len) { 3         char ta[] = value; 4         int to = toffset; 5         char pa[] = other.value; 6         int po = ooffset; 7         // Note: toffset, ooffset, or len might be near -1>>>1. 8         if ((ooffset < 0) || (toffset < 0) 9                 || (toffset > (long)value.length - len)10                 || (ooffset > (long)other.value.length - len)) {11             return false;12         }13         while (len-- > 0) {14             char c1 = ta[to++];15             char c2 = pa[po++];16             if (c1 == c2) {17                 continue;18             }19             if (ignoreCase) {20                 // If characters don‘t match but case may be ignored,21                 // try converting both characters to uppercase.22                 // If the results match, then the comparison scan should23                 // continue.24                 char u1 = Character.toUpperCase(c1);25                 char u2 = Character.toUpperCase(c2);26                 if (u1 == u2) {27                     continue;28                 }29                 // Unfortunately, conversion to uppercase does not work properly30                 // for the Georgian alphabet, which has strange rules about case31                 // conversion.  So we need to make one last check before32                 // exiting.33                 if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {34                     continue;35                 }36             }37             return false;38         }39         return true;40     }

 

Java String類中CaseInsensitiveComparator.compare()方法的實現