?? groupinpat.html
字號:
<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<TITLE>Using the Captured Text of a Group within a Pattern
(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">
<STYLE TYPE="text/css">
<!-- BODY CODE {font-family: Courier, Monospace; font-size: 11pt} TABLE, BODY {font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 10pt} PRE {font-family: Courier, Monospace; font-size: 10pt} H3 {font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 11pt} A.eglink {text-decoration: none} A:hover.eglink {text-decoration: underline} -->
</STYLE>
</HEAD>
<BODY>
<TABLE CELLSPACING="0" CELLPADDING="0" BORDER="0">
<TR>
<TD rowspan="3"><A HREF="/?l=ex"><IMG BORDER="0" ALIGN="BOTTOM" HSPACE="10" SRC="/egs/almanac14a.jpg"></A></TD><TD VALIGN="top"><font face="Times" size="6"><b>The Java Developers Almanac 1.4</b></font>
<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">
<DIV ALIGN="LEFT">
<A HREF="/">Home</A>
>
<A HREF="../index.html">List of Packages</A>
>
<B><A HREF="../java.util.regex/pkg.html">java.util.regex</A></B><font color="#666666" SIZE="-2">
[26 examples]
</font>
>
<B><A HREF="../java.util.regex/pkg.html#Groups">Groups</A></B><font color="#666666" SIZE="-2">
[5 examples]
</font>
</DIV><P>
<h3>
e439.
Using the Captured Text of a Group within a Pattern</h3>
It is possible to use the value of a group within the same pattern.
For example, suppose you're trying to extract the text between some
XML tags and you don't know what the possible sets of tags are.
However, you do know that the tag name appears in both the start and
end tags. How do you take the dynamically matched tag name from
the start tag and use it in the end tag?
<P> Back references can be used in this scenario. A back reference
refers to a capture group (see <a href="../java.util.regex/Group.html" class="eglink"><font size="-1"><b>e436</b> Capturing Text in a Group in a Regular Expression</font></a>)
within the pattern. It has the form <code>\n</code> where <code>n</code> is a group number
starting from 1. The back reference should not be contained in or
precede the named group.
<pre>
// Compile regular expression with a back reference to group 1
String patternStr = <font color="#0066ff"><i>"<(\\S+?).*?>(.*?)</\\1>"</i></font>;
Pattern pattern = Pattern.compile(patternStr);
Matcher matcher = pattern.matcher("");
// Set the input
matcher.reset(<font color="#0066ff"><i>"xx <tag a=b> yy </tag> zz"</i></font>);
// Get tagname and contents of tag
boolean matchFound = matcher.find(); // true
String tagname = matcher.group(1); // tag
String contents = matcher.group(2); // yy
matcher.reset(<font color="#0066ff"><i>"xx <tag> yy </tag0>"</i></font>);
matchFound = matcher.find(); // false
</pre>
<P><table width="600" CELLSPACING="0" CELLPADDING="2" BORDER="0">
<tr>
<td bgcolor="#6666cc" align="center"><font color="#ffffff">
Related Examples
</font></td>
</tr>
</table>
e436. <a class="eglink" href="Group.html?l=rel">
Capturing Text in a Group in a Regular Expression
</a>
<br>
e437. <a class="eglink" href="GroupIx.html?l=rel">
Getting the Indices of a Matching Group in a Regular Expression
</a>
<br>
e438. <a class="eglink" href="NoGroup.html?l=rel">
Using a Non-Capturing Group in a Regular Expression
</a>
<br>
e440. <a class="eglink" href="GroupInRep.html?l=rel">
Using the Captured Text of a Group within a Replacement Pattern
</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#Flags">
Flags
</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 FACE="Verdana, Arial, Helvetica, sans-serif" SIZE="0">
© 2002 Addison-Wesley.
</FONT>
</BODY>
</HTML>
?? 快捷鍵說明
復(fù)制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -