Java 基础类型 —— Character

偏执的太偏执、 2023-05-29 05:20 1阅读 0赞

### 文章目录 ###

*   *  1 char 数据类型概述
     *  2 Character 数据类型概述
     *  3 Character 方法简述
     *   *  3.1 是否有效 或 为 Surrogate 类型
         *  3.2 特定下标(之前)的 code point 值
         *  3.3 codepoint 与 surrogate 的转换
         *  3.4 因为 surrogate 导致的统计个数
         *  3.5 codepoint 代表的类型 General category
         *  3.6 杂
         *  3.7 toLowerCase / toUpperCase /toTitleCase
     *  参考

## 1 char 数据类型概述 ##

*  码点（code point）：unicode 字符集中字符对应的数值
 *  在Java中,char 数据类型（和 Character 对象封装的值）基于原始的 Unicode 规范（字符集）
 *  char表示 UTF-16 编码的代码单元 (code unit)
 *  对于0号平面(BMP),一个码点(code point)对应 1 个 code unit —— 1 个 char 对应一个 unicode 字符集中的字符
 *  对于辅助平面,一个 code point 将会对应 2 个 code unit—— 2 个 char 对应一个 unicode 字符集中的字符

## 2 Character 数据类型概述 ##

*  Character在 jdk8中, 基于版本Unicode6.0.2 标准
 *  Character 类的方法和数据是通过 UnicodeData 文件中的信息定义的
 *  此文件指定了各种属性，其中包括每个已定义 Unicode 代码点或字符范围的名称和常规类别(General category)
 *  详情可查阅 http://www.unicode.org

## 3 Character 方法简述 ##

### 3.1 是否有效 或 为 Surrogate 类型 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>简述</th> 
   <th>补充</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static boolean</td> 
   <td>isValidCodePoint(int var0)</td> 
   <td>是否为有效的codePoint</td> 
   <td>(var0 &gt;&gt;&gt; 16) &lt; 17</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isBmpCodePoint(int var0)</td> 
   <td>是否在第 0 平面</td> 
   <td>var0 &gt;&gt;&gt; 16 == 0</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isSupplementaryCodePoint(int var0)</td> 
   <td>是否在辅助平面</td> 
   <td>var0 &gt;= 0x10000&amp;&amp; var0 &lt; 0x110000;</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isHighSurrogate(char var0)</td> 
   <td>是否是高代理</td> 
   <td>var0 &gt;= ‘\ud800’ &amp;&amp; var0 &lt; ‘\udc00’</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isLowSurrogate(char var0)</td> 
   <td>是否是低代理</td> 
   <td>var0 &gt;= ‘\udc00’ &amp;&amp; var0 &lt; ‘\ue000’</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isSurrogate(char var0)</td> 
   <td>是否是代理</td> 
   <td>综上</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isSurrogatePair(char var0, char var1)</td> 
   <td>是否是代理对</td> 
   <td>isHighSurrogate(var0) &amp;&amp; isLowSurrogate(var1)</td> 
  </tr> 
 </tbody> 
</table>

### 3.2 特定下标(之前)的 code point 值 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>返回类型方法名</th> 
   <th>简述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static int</td> 
   <td>codePointAt(CharSequence seq, int index)</td> 
   <td>获取指定位置的 codePoint</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointAt(char[] var0, int var1)</td> 
   <td>同上</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointAt(char[] var0, int var1, int var2)</td> 
   <td>同上，加范围限制</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointBefore(CharSequence var0, int var1)</td> 
   <td>获取前一个位置的 codePoint</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointBefore(char[] var0, int var1)</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointBefore(char[] var0, int var1, int var2)</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

### 3.3 codepoint 与 surrogate 的转换 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>简述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static char[]</td> 
   <td>toChars(int var0)</td> 
   <td>将 codePoint 转为数组</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>toChars(int var0, char[] var1, int var2)</td> 
   <td>保存到数组的指定位置</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>toCodePoint(char var0, char var1)</td> 
   <td>将 surrogatePair 合成为 codePoint,这之前要检查 surrogatePair 类型</td> 
  </tr> 
  <tr> 
   <td>static char</td> 
   <td>highSurrogate(int var0)</td> 
   <td>返回代码点的高代理</td> 
  </tr> 
  <tr> 
   <td>static char</td> 
   <td>lowSurrogate(int var0)</td> 
   <td>返回代码点的低代理</td> 
  </tr> 
 </tbody> 
</table>

### 3.4 因为 surrogate 导致的统计个数 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>简述</th> 
   <th>补充</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static int</td> 
   <td>charCount(int var0)</td> 
   <td>codePoint 对应的 char 的个数</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointCount(CharSequence var0, int var1, int var2)</td> 
   <td>v1-v2 之间的 <strong>codePoint</strong> 的个数</td> 
   <td>不是 char 的个数</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>codePointCount(char[] var0, int var1, int var2)</td> 
   <td>同上</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>offsetByCodePoints(CharSequence var0, int var1, int var2)</td> 
   <td>返回偏移指定个数的 <strong>codepoint</strong> 后的索引</td> 
   <td>由于 codepoint 可能对应 2 个 char，索引不能简单的直加</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>offsetByCodePoints(char[] var0, int var1, int var2, int var3, int var4)</td> 
   <td>同上，加限制了</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

### 3.5 codepoint 代表的类型 General category ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>简述</th> 
   <th>补充</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static boolean</td> 
   <td>isLowerCase(int var0)</td> 
   <td>小写?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isUpperCase(int var0)</td> 
   <td>大写?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isTitleCase(int var0)</td> 
   <td>首字母大写?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isDigit(int var0)</td> 
   <td>数字?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isDefined(int var0)</td> 
   <td>被定义为 Unicode 中的字符?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isLetter(int var0)</td> 
   <td>字母?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isLetterOrDigit(int var0)</td> 
   <td>字母或数字?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isJavaLetter(char var0)</td> 
   <td></td> 
   <td>isJavaIdentifierStart(var0)</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isJavaLetterOrDigit(char var0)</td> 
   <td></td> 
   <td>isJavaIdentifierPart(var0)</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isAlphabetic(int var0)</td> 
   <td>比 isLetter 大一些</td> 
   <td>确定指定的字符（Unicode代码点）是否是字母表</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isIdeographic(int var0)</td> 
   <td></td> 
   <td>是否是Unicode标准定义的CJKV（中文，日文，韩文和越南文）表意文字</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td><strong>isJavaIdentifierStart</strong>(int var0)</td> 
   <td>The “Java letters” include uppercase and lowercase ASCII Latin letters A-Z (\u0041- \u005a), and a-z (\u0061-\u007a),</td> 
   <td>and, for historical reasons, the ASCII underscore (_, or \u005f) and dollar sign ($, or \u0024).</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isJavaIdentifierPart(int var0)</td> 
   <td>比上面多了数字</td> 
   <td><a href="https://docs.oracle.com/javase/specs/jls/se8/jls8.pdf" rel="nofollow">参考 3.8 章节</a></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isUnicodeIdentifierStart(int var0)</td> 
   <td>是否允许作为 Unicode 标识符中的首字符?</td> 
   <td>isLetter || LETTER_NUMBER</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isUnicodeIdentifierPart(int var0)</td> 
   <td>是否允许作为 Unicode 标识符中的首字符以外的字符?</td> 
   <td>不懂</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isIdentifierIgnorable(int var0)</td> 
   <td>是否是 Java 标识符或 Unicode 标识符中可忽略的一个字符?</td> 
   <td>不懂</td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isSpaceChar(int var0)</td> 
   <td>unicode 中的空白字符?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isWhitespace(int var0)</td> 
   <td>Java 中的空白字符?</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isISOControl(int var0)</td> 
   <td>是否是ISO控制字符</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static boolean</td> 
   <td>isMirrored(int var0)</td> 
   <td>是否镜像</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

### 3.6 杂 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>返回类型</th> 
   <th>简述</th> 
   <th>补充</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static String</td> 
   <td>String getName(int codePoint)</td> 
   <td>static String</td> 
   <td>返回codepoint 所属类型的名称</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>getNumericValue(int codePoint)</td> 
   <td>static int</td> 
   <td>返回指定的Unicode字符代表的罗马数值</td> 
   <td>字符’\ u216C’(罗马数字50)将返回一个int 值50</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>digit(int codePoint, int radix)</td> 
   <td>static int</td> 
   <td>codePoint 对应 radix 进制 的数值</td> 
   <td>因为 0-9 + a-z，总数是 36，所以 2&lt;=radix&lt;=35； digit(‘h’,20)==17</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>char forDigit(int digit,int radix)</td> 
   <td>static int</td> 
   <td>digit 对应的进制的字符</td> 
   <td>forDigit(17,20)==‘h’</td> 
  </tr> 
  <tr> 
   <td>static Character</td> 
   <td>valueOf(char c)</td> 
   <td>static Character</td> 
   <td>返回包装类型</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static char</td> 
   <td>reverseBytes(char ch)</td> 
   <td>static char</td> 
   <td>返回通过反转指定的 char值中的字节顺序获得的值</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>getType(int var0)</td> 
   <td>static int</td> 
   <td>返回 codepoint 类型</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>static byte</td> 
   <td>getDirectionality(int var0)</td> 
   <td>static byte</td> 
   <td>给定字符的Unicode方向性属性</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

### 3.7 toLowerCase / toUpperCase /toTitleCase ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>简述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static int</td> 
   <td>toLowerCase(int codePoint)</td> 
   <td>返回对应的小写的 codepoint</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>toUpperCase(int codePoint)</td> 
   <td>返回对应的大写的 codepoint</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>toUpperCaseEx(int codePoint)</td> 
   <td>如果错误，返回 ERROR 代码</td> 
  </tr> 
  <tr> 
   <td>static char[]</td> 
   <td>toUpperCaseCharArray(int codePoint)</td> 
   <td>返回 char[] 形式</td> 
  </tr> 
  <tr> 
   <td>static char</td> 
   <td>toTitleCase(int codePoint)</td> 
   <td>不懂</td> 
  </tr> 
 </tbody> 
</table>

## 参考 ##

jdk 1.8\_171

[官方 API][API]

[基础数据类型之Character][Character]

[API]: https://docs.oracle.com/javase/8/docs/api/java/lang/Character.html
[Character]: https://www.cnblogs.com/noteless/p/9801803.html