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

最新推荐文章于 2024-05-02 13:31:52 发布

转载最新推荐文章于 2024-05-02 13:31:52 发布 · 338 阅读

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原文链接：http://www.cnblogs.com/yanyichao/p/4493039.html

文章标签：

#java

本文介绍了一种实现字符串大小写不敏感比较的方法，并详细解释了如何通过转换为大写和小写进行比较以兼容格鲁吉亚字符，同时给出了具体的Java代码示例。

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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     }