如何在 Java 正则表达式中使用反向引用答案

【问题标题】：How to use back reference in Java regex如何在 Java 正则表达式中使用反向引用
【发布时间】：2014-10-15 21:55:32
【问题描述】：

RE 专家的问题：考虑以下 Perl 脚本：

my @lines = (
        "Once upon a time in a galaxy far, far away, there lived\n",
        "this _idiot_ trying to _mark up_ a few lines of\n",
        "marked down text using yet another _language_.\n");

foreach (@lines) {
        s|_(.+?)_|<em>$1</em>|g;
        print
}

% perl [aboveScript] 的输出是

Once upon a time in a galaxy far, far away, there lived
this <em>idiot</em> trying to <em>mark up</em> a few lines of
marked down text using yet another <em>language</em>.

我正在尝试在 Java 中实现这一点。我想出的课程如下。它有效，我得到与上面相同的输出，但我很确定这不是这样做的方法。我的问题 - 你将如何实现“parseLine()”方法？

import java.util.*;
import java.util.regex.*;

public class Reglob {

        private final static Pattern emPattern = Pattern.compile ("_(.+?)_");

        public void parseLine (String[] lines) {
                for (String line : lines) {
                        List<Integer>   bList = new ArrayList<Integer>(),
                                        eList = new ArrayList<Integer>();
                        Matcher m = emPattern.matcher (line);
                        int n = 0;
                        while (m.find()) {
                                // System.out.println ("Match indices: " + m.start() + ", " + m.end());
                                bList.add (m.start());
                                eList.add (m.end());
                                n++;
                        }
                        if (n == 0) {
                                System.out.println (line);
                        } else {
                                String s = line.substring (0, bList.get(0));
                                for (int i = 0 ; i < n-1 ; i++) {
                                    s += "<em>"
                                        + line.substring(1+bList.get(i),eList.get(i)-1)
                                        + "</em>" + line.substring (eList.get(i), bList.get(i+1));
                                }
                                s += "<em>"
                                        + line.substring(1+bList.get(n-1),eList.get(n-1)-1)
                                        + "</em>" + line.substring (eList.get(n-1), line.length());
                                System.out.println (s);
        }}}

        public static void main (String[] args) {
                String[] lines = {
                        "Once upon a time in a galaxy far, far away, there lived",
                        "this _idiot_ trying to _mark up_ a few lines of",
                        "marked down text using yet another _language_."};
                new Reglob().parseLine (lines);
}}

【问题讨论】：

Java; String replace (using regular expressions)?的可能重复
这个问题只有专家才能回答？我觉得受到了歧视……
@200_success 的欺骗被豆腐啤酒回答了。我怎么错过了豆腐啤酒？ Can Berk Güder 的另一个答案，听起来像是另一种异国情调的啤酒，也许是瑞典的，而且很好。
Java 正则表达式中除了我自己之外的任何人都是专家 - 我只是一个新手。现在我明白了……这么多正确答案，不知道该选哪一个！我什至不需要这个模式 - 哦，好吧！

标签： java regex

【解决方案1】：

这是您的 Perl 脚本的 Java 等价物：

public class Main {
    public static void main(String[] args) {
        String[] lines = {
                "Once upon a time in a galaxy far, far away, there lived\n",
                "this _idiot_ trying to _mark up_ a few lines of\n",
                "marked down text using yet another _language_.\n" };

        for(String line : lines) {
            String output = line.replaceAll("_(.+?)_", "<em>$1</em>");

            System.out.print(output);
        }
    }
}

它输出：

Once upon a time in a galaxy far, far away, there lived
this <em>idiot</em> trying to <em>mark up</em> a few lines of
marked down text using yet another <em>language</em>.

【讨论】：

【解决方案2】：

你可以这样做，

String [] s = {  "Once upon a time in a galaxy far, far away, there lived",
                "this _idiot_ trying to _mark up_ a few lines of",
                 "marked down text using yet another _language_."};
for(String s2 : s)
{
System.out.println(s2.replaceAll("_([^_]+)_", "<em>$1</em>"));
}

【讨论】：

【解决方案3】：

试试这样的：

public static final String str = "Once upon a time in a galaxy far, far away, there lived\n" +
        "this _idiot_ trying to _mark up_ a few lines of\n" +
        "marked down text using yet another _language_.\n";

public static void main(String[] args) {
    System.out.println(str.replaceAll("_(.+?)_", "<em>$1</em>"));
}

这个的输出：

Once upon a time in a galaxy far, far away, there lived
this <em>idiot</em> trying to <em>mark up</em> a few lines of
marked down text using yet another <em>language</em>.

【讨论】：

【解决方案4】：

同样，在 Scala 中：

scala> val text = """Once upon a time in a galaxy far, far away, there lived
     | this _idiot_ trying to _mark up_ a few lines of
     | marked down text using yet another _language_."""
text: String =
Once upon a time in a galaxy far, far away, there lived
this _idiot_ trying to _mark up_ a few lines of
marked down text using yet another _language_.

scala> val r = "_(.+?)_".r
r: scala.util.matching.Regex = _(.+?)_

scala> r.replaceAllIn(text, """<em>$1<\em>""")
res3: String =
Once upon a time in a galaxy far, far away, there lived
this <em>idiot<em> trying to <em>mark up<em> a few lines of
marked down text using yet another <em>language<em>.

我首先在 Scala REPL 中尝试一切，然后转换为 Java。

但既然你有很多 Java 答案，我会回到 Hulu。

【讨论】：