概述
CaseFormat用来转换各种不同的编程语言间的变量名命名格式, 主要用到的方法只有一个 CaseFormat.to(CaseFormat from, String s)
CaseFormat fromFormat = CaseFormat.LOWER_CAMEL;
CaseFormat toFormat = CaseFormat.UPPER_CAMEL;
String s = "lowerCamel";
System.out.println(fromFormat.to(toFormat, s));
输出
代码分析
package com.google.common.base; import com.google.common.annotations.GwtCompatible; /**
* Utility class for converting between various ASCII case formats.
* 转换ASCII字符串各种格式的工具类
*
* @author Mike Bostock
* @since 1.0
*/
@GwtCompatible
public enum CaseFormat {
/**
* Hyphenated variable naming convention, e.g., "lower-hyphen".
* 带连接符的变量名转换
*/
LOWER_HYPHEN(CharMatcher.is('-'), "-"), /**
* C++ variable naming convention, e.g., "lower_underscore".
* C++ 变量名转换
*/
LOWER_UNDERSCORE(CharMatcher.is('_'), "_"), /**
* Java variable naming convention, e.g., "lowerCamel".
* Java 变量名转换
*/
LOWER_CAMEL(CharMatcher.inRange('A', 'Z'), ""), /**
* Java and C++ class naming convention, e.g., "UpperCamel".
* Java 和 C++ 类名转换
*/
UPPER_CAMEL(CharMatcher.inRange('A', 'Z'), ""), /**
* Java and C++ constant naming convention, e.g., "UPPER_UNDERSCORE".
* Java 和 C++ 常量命名转换
*/
UPPER_UNDERSCORE(CharMatcher.is('_'), "_"); private final CharMatcher wordBoundary;
private final String wordSeparator; CaseFormat(CharMatcher wordBoundary, String wordSeparator) {
this.wordBoundary = wordBoundary;
this.wordSeparator = wordSeparator;
} /**
* Converts the specified {@code String s} from this format to the specified {@code format}. A
* "best effort" approach is taken; if {@code s} does not conform to the assumed format, then the
* behavior of this method is undefined but we make a reasonable effort at converting anyway.
*
* 使用这个format将指定String s转为指定format.采取的是"尽力而为"的方法;假如s不符合设定的格式
* 那么这个方法的行为将会是不确定的,但我们会尽量做出合理的转换
*
* 实际上我们使用的只有这一个方法
*/
public String to(CaseFormat format, String s) {
if (format == null) {
throw new NullPointerException();
}
if (s == null) {
throw new NullPointerException();
} if (format == this) {
return s;
} /* optimize cases where no camel conversion is required */
/* 没有驼峰转换的时候优化转换 */
switch (this) {
case LOWER_HYPHEN:
switch (format) {
case LOWER_UNDERSCORE:
return s.replace('-', '_');
case UPPER_UNDERSCORE:
return Ascii.toUpperCase(s.replace('-', '_'));
}
break;
case LOWER_UNDERSCORE:
switch (format) {
case LOWER_HYPHEN:
return s.replace('_', '-');
case UPPER_UNDERSCORE:
return Ascii.toUpperCase(s);
}
break;
case UPPER_UNDERSCORE:
switch (format) {
case LOWER_HYPHEN:
return Ascii.toLowerCase(s.replace('_', '-'));
case LOWER_UNDERSCORE:
return Ascii.toLowerCase(s);
}
break;
} // otherwise, deal with camel conversion
// 处理驼峰转其他的转换
StringBuilder out = null;
int i = 0;
int j = -1;
// 将字符串按分隔符切分单词,转换每个单词
while ((j = wordBoundary.indexIn(s, ++j)) != -1) {
if (i == 0) {
// include some extra space for separators
// 为分隔符留出额外的空间
out = new StringBuilder(s.length() + 4 * wordSeparator.length());
// 第一个单词使用normalizeFirstWord处理
out.append(format.normalizeFirstWord(s.substring(i, j)));
} else {
// 后续单词用normalizeWord处理
out.append(format.normalizeWord(s.substring(i, j)));
}
out.append(format.wordSeparator);
// 当前坐标后移
i = j + wordSeparator.length();
}
if (i == 0) {
return format.normalizeFirstWord(s);
}
// 处理最后一个分隔符右边的字符串
out.append(format.normalizeWord(s.substring(i)));
return out.toString();
} /**
* 将第一个单词普通化
* LOWER_CAMEL -> 全小写
* 其他 -> normalizeWord
*/
private String normalizeFirstWord(String word) {
switch (this) {
case LOWER_CAMEL:
return Ascii.toLowerCase(word);
default:
return normalizeWord(word);
}
} /**
* 将单词普通化
* LOWER_HYPHEN, LOWER_UNDERSCORE -> 全小写
* LOWER_CAMEL, UPPER_CAMEL -> 第一个字母大写其他字母小写
* UPPER_UNDERSCORE -> 全大写
*/
private String normalizeWord(String word) {
switch (this) {
case LOWER_HYPHEN:
return Ascii.toLowerCase(word);
case LOWER_UNDERSCORE:
return Ascii.toLowerCase(word);
case LOWER_CAMEL:
return firstCharOnlyToUpper(word);
case UPPER_CAMEL:
return firstCharOnlyToUpper(word);
case UPPER_UNDERSCORE:
return Ascii.toUpperCase(word);
}
throw new RuntimeException("unknown case: " + this);
} /**
* 将单词第一个字母变大写,其他变小写
*/
private static String firstCharOnlyToUpper(String word) {
int length = word.length();
if (length == 0) {
return word;
}
return new StringBuilder(length)
.append(Ascii.toUpperCase(word.charAt(0)))
.append(Ascii.toLowerCase(word.substring(1)))
.toString();
}
}