Java String类中CaseInsensitiveComparator.compare()方法的实现

String对象的大小写不敏感比较方法的实现如下：

 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 promotion
16                             return c1 - c2;
17                         }
18                     }
19                 }
20             }
21             return n1 - n2;
22         }

这里，同时比较了UpperCase和LowerCase，是为了兼容Georgian字符。

见String类的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 should
23                 // 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 properly
30                 // for the Georgian alphabet, which has strange rules about case
31                 // conversion.  So we need to make one last check before
32                 // exiting.
33                 if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
34                     continue;
35                 }
36             }
37             return false;
38         }
39         return true;
40     }

 

posted @ 2015-05-10 20:52  yanyichao  阅读(1859)  评论(0)  编辑  收藏  举报