我写了code匹配的文件路径具有extenstion .ncx，

 模式= Pattern.compile（$（\\ | \ /）[A-ZA-Z0-9 _] / NCX。）;
 匹配器匹配= pattern.mather（\ sample.ncx）;
 

这显示了一个无效的转义序列（有效的是\ B \吨\ñ\ F \ r \\'\）语法错误的图案。我怎样才能解决这个问题。

 模式P = Pattern.compile（[/ \\\\]（[A-ZA-Z0-9 _ ] + \\ NCX）$）。
匹配器米= p.matcher（\\ sample.ncx）;
如果（m.find（））
{
  System.out.printf（文件名是'％s'的％N，m.group（1））;
}
 

输出：

 的文件名是'sample.ncx
 

$ 锚的比赛到字符串的末尾（或在多行模式的行的结尾）。它属于在的结束你的正则表达式的的，而不是开始。

[/ \\\\] 是字符类匹配一个斜杠或反斜杠。反斜线必须是双转义，因为它具有特殊的意义无论是在正则表达式和一个字符串。正斜杠做的没有的要求逃脱。

[A-ZA-Z0-9 _] + 匹配一个或多个列出的字符;未经加号，你只匹配的一个的。

第二个斜杠在你的正则表达式是没有意义的，但你需要一个反斜杠有逃脱的点的当然是 - 并且，反斜线来转义为Java字符串。

由于我从交替切换（ | ）以字符类的斜线，已不再需要在你的正则表达式的括号内。相反，我用它们来捕捉中的实际文件名，只是为了演示如何这样做了。

I wrote code for matching filepath which have extenstion .ncx ,

 pattern = Pattern.compile("$(\\|\/)[a-zA-Z0-9_]/.ncx");
 Matcher matcher = pattern.mather("\sample.ncx");

This shows a invalid escape sequence (valid ones are \b \t \n \f \r \" \' \ ) syntax error pattern. How can I fix it.

Pattern p = Pattern.compile("[/\\\\]([a-zA-Z0-9_]+\\.ncx)$");
Matcher m = p.matcher("\\sample.ncx");
if (m.find())
{
  System.out.printf("The filename is '%s'%n", m.group(1));
}

output:

The filename is 'sample.ncx'

$ anchors the match to the end of the string (or to the end of a line in multiline mode). It belongs at the end of your regex, not the beginning.

[/\\\\] is a character class that matches a forward-slash or a backslash. The backslash has to be double-escaped because it has special meaning both in a regex and in a string literal. The forward-slash does not require escaping.

[a-zA-Z0-9_]+ matches one or more of the listed characters; without the plus sign, you were only matching one.

The second forward-slash in your regex makes no sense, but you do need a backslash there to escape the dot--and of course, the backslash has to be escaped for the Java string literal.

Because I switched from the alternation (|) to a character class for the leading slash, the parentheses in your regex were no longer needed. Instead, I used them to capture the actual filename, just to demonstrate how that's done.