📄 comment.htm
字号:
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<TITLE>Adding Comments to a Regular Expression (Java Developers Almanac Example)
</TITLE>
<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
<META CONTENT="Addison-Wesley/Patrick Chan" NAME="OWNER">
<META CONTENT="3/20/02" NAME="revision">
<META CONTENT="no-cache" HTTP-EQUIV="Pragma">
<LINK href="/almanac.css" media="screen" type="text/css" rel="stylesheet">
</HEAD>
<BODY>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD></TD>
</TR>
</TABLE>
<br>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD></TD>
</TR>
<TR>
<TD rowspan="3"><A HREF="/?l=ex"><IMG BORDER="0" ALIGN="BOTTOM" HSPACE="10" SRC="/egs/almanac14a.jpg"></A></TD><TD VALIGN="top">
<h1>The Java Developers Almanac 1.4</h1>
<br>
Order this book from <a href="/cgi-bin/scripts/redirect.pl?l=ex&url=http://www.amazon.com/exec/obidos/ASIN/0201752808/xeo">Amazon</a>.
</TD>
</TR>
<TR>
<TD align="right" valign="bottom">
<FORM method="get" action="/cgi-bin/search/find.pl">
<INPUT size="25" name="words" type="text"><INPUT value="Search" type="submit">
</FORM>
</TD>
</TR>
</TABLE>
<HR color="#6666cc">
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD valign="top"><script type="text/javascript">
<!--
google_ad_client = "pub-6001183370374757";
google_ad_width = 120;
google_ad_height = 600;
google_ad_format = "120x600_as";
google_ad_channel = "4777242811";
google_ad_type = "text_image";
google_color_border = "FFFFFF";
google_color_bg = "FFFFFF";
google_color_link = "6666CC";
google_color_url = "6666CC";
google_color_text = "000000";
//--></script><script src="http://pagead2.googlesyndication.com/pagead/show_ads.js" type="text/javascript"></script></TD><TD> </TD><TD valign="top">
<DIV ALIGN="LEFT">
<A HREF="/">Home</A>
>
<A HREF="../index.html">List of Packages</A>
>
<A HREF="../java.util.regex/pkg.html">java.util.regex</A><font color="#666666" class="xsmall-font">
[26 examples]
</font>
>
<B><A HREF="../java.util.regex/pkg.html#Flags">Flags</A></B><font color="#666666" class="xsmall-font">
[3 examples]
</font>
</DIV><P>
<h3>e434. Adding Comments to a Regular Expression</h3>
By default, whitespace in a regular expression is significant. By
specifying the <code>COMMENTS</code> flag, whitespace can be ignored in a pattern.
While in comment mode, a particular whitespace character can be
matched using a character class (for example, [\ ] matches a space).
<P> In comment mode, the <code>#</code> character and everything
following it is ignored. This feature is useful when a pattern is read
from a file. Comment mode allows the pattern to span multiple lines
and be commented.
<P> It is also possible to enable comments within a pattern using
the inline modifier <code>(?x)</code>. The inline modifier affects all
characters to the right and in the same enclosing group, if any. For
example, in the pattern <code>a(b(?x)c)d</code>, only <code>c</code> is allowed to
have comments. You can also force no comments with <code>(?-x)</code>.
<P> The inline modifier can also contain pattern characters using
the form <code>(?x:abc)</code>. In this case, only those pattern characters
inside the inline modifier's enclosing group are affected. This form
does not capture text (see <a href="../java.util.regex/Group.html" class="eglink"><b>e436</b> Capturing Text in a Group in a Regular Expression</a>).
<pre> CharSequence inputStr = <font color="#0066ff"><i>"a b"</i></font>;
String patternStr = <font color="#0066ff"><i>"a b"</i></font>;
// Compile without comments
Pattern pattern = Pattern.compile(patternStr);
Matcher matcher = pattern.matcher(inputStr);
boolean matchFound = matcher.matches(); // true
// Compile with comments
pattern = Pattern.compile(patternStr, Pattern.COMMENTS);
matcher = pattern.matcher(inputStr);
matchFound = matcher.matches(); // false
// Use COMMENTS but include a character class with a space
patternStr = <font color="#0066ff"><i>"a [\\ ] b"</i></font>;
pattern = Pattern.compile(patternStr, Pattern.COMMENTS);
matcher = pattern.matcher(inputStr);
matchFound = matcher.matches(); // true
// Use an inline modifier
matchFound = pattern.matches(<font color="#0066ff"><i>"a b"</i></font>, inputStr); // true
matchFound = pattern.matches(<font color="#0066ff"><i>"(?x)a b"</i></font>, inputStr); // false
matchFound = pattern.matches(<font color="#0066ff"><i>"(?x)a [\\ ] b"</i></font>, inputStr); // true
matchFound = pattern.matches(<font color="#0066ff"><i>"(?x)a \\s b"</i></font>, inputStr); // true
matchFound = pattern.matches(<font color="#0066ff"><i>"a (?x: b )"</i></font>, inputStr); // true
// Tabs and newlines in the pattern are ignored as well
matchFound = pattern.matches(<font color="#0066ff"><i>"(?x)a \t\n \\s b"</i></font>, inputStr); // true
// Read pattern from file
try {
File f = new File(<font color="#0066ff"><i>"pattern.txt"</i></font>);
FileReader rd = new FileReader(f);
char[] buf = new char[(int)f.length()];
rd.read(buf);
patternStr = new String(buf);
matcher = pattern.matcher(inputStr);
matchFound = matcher.matches(); // true
} catch (IOException e) {
}
</pre>
Here are the contents of pattern.txt:
<pre> # This pattern matches ``a b''
a # this is the first part
[\ ] # this is the second part
b # this is the third part
</pre>
<P><table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td bgcolor="#6666cc" align="center"><font color="#ffffff">
<b>Related Examples</b></font></td>
</tr>
</table>
e433. <a class="eglink" href="Case.html?l=rel">
Setting Case Sensitivity in a Regular Expression
</a>
<br>
e435. <a class="eglink" href="MultiFlags.html?l=rel">
Compiling a Pattern with Multiple Flags
</a>
<br>
<table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td align="left">
<br>
See also:
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Groups">
Groups
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Lines">
Lines
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Paragraphs">
Paragraphs
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Searching%20and%20Replacing">
Searching and Replacing
</a>
<a class="eglink" href="/egs/java.util.regex/pkg.html?l=rel#Tokenizing">
Tokenizing
</a>
</td>
</tr>
</table>
<br>
<br>
<FONT class="xsmall-font">
© 2002 Addison-Wesley.
</FONT></TD><TD> </TD><TD valign="top"><A href="http://compositesw.com/devzone?ref=javaalmanac"><IMG alt="Click Here" height="600" width="120" border="0" src="/csw_oad_120x600_final.gif"></A></TD>
</TR>
</TABLE>
</BODY>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<META CONTENT="NO-CACHE" HTTP-EQUIV="PRAGMA">
</HEAD>
</HTML>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -