java - 为什么会出现 java.lang.IllegalArgumentException？

Question

我的程序每次运行时都会打印一个 java.lang.IllegalArgumentException。它用不同的表达式替换某些模式，包括它匹配的模式中的组。它替换了一部分模式，然后出现此错误:

Exception in thread "main" java.lang.IllegalArgumentException: Illegal group reference
    at java.util.regex.Matcher.appendReplacement(Matcher.java:713)
    at RealReadFile.main(RealReadFile.java:93)

这是我的代码:

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.io.FileNotFoundException;
import java.io.File;

public class RealReadFile {
    private static final String fileName = "KLSadd.tex";
    private Scanner myFile = null;

    public RealReadFile() throws FileNotFoundException {
        if (myFile == null)
            myFile = new Scanner(new File(fileName));
    }

    public RealReadFile(String name) throws FileNotFoundException {
        if (myFile != null)
            myFile.close();
        myFile = new Scanner(new File(name));
    }

    public boolean endOfFile() { 
        return !myFile.hasNext(); 
    }

    public String nextLine() {
        return myFile.nextLine().trim();
    }

    public int times(String oneline){
            int count = 0;
            Pattern cpochhammer = Pattern.compile("(\\(([^\\)]+)\\)_\\{?([^\\}]+)\\}?)");
            Matcher pochhammer = cpochhammer.matcher(oneline);
            while (pochhammer.find()) {
                count++;
            }   
        return count;
    }

    public void multipleChar(RealReadFile file){
        while (!file.endOfFile()) {
            String line = file.nextLine();
            int count=file.times(line);
            while(count>0){
                Pattern cpochhammer = Pattern.compile("(\\(([^\\)]+)\\)_\\{?([^\\}]+)\\}?)");
                Matcher pochhammer = cpochhammer.matcher(line);
                if (pochhammer.find()) {
                    //System.out.println(line);
                    line = pochhammer.replaceFirst("\\\\pochhammer{"+ pochhammer.group(2) + "}{" + pochhammer.group(3) + "}");
                    count--;
                    }
                if(count==0)
                    System.out.println(line);
                }
            }
    }

    public void singleChar(RealReadFile file){
        while (!file.endOfFile()) {
            String line = file.nextLine();
            int count=file.times(line);
            while(count>0){
            Pattern cpochhammer = Pattern.compile("(\\(([^\\)]+)\\)_(.))");
            Matcher pochhammer = cpochhammer.matcher(line);
            if (pochhammer.find()) {
                //System.out.println(line);
              line = pochhammer.replaceFirst("\\\\pochhammer{"
                        + pochhammer.group(2) + "}{" + pochhammer.group(3)
                        + "}");
                count--;
            }
            if(count==0)
                System.out.println(line);
            }
            }
    }
    public boolean checkMultiple(String line){
        Pattern cpochhammer = Pattern.compile("(\\(([^\\)]+)\\)_\\{([^\\}]+)\\})");
        Matcher pochhammer = cpochhammer.matcher(line);
        if(pochhammer.find())
            return true;
        return false;
    }

    public static void main(String[] args) throws FileNotFoundException {
        RealReadFile file = new RealReadFile();
        while (!file.endOfFile()) {
            String line = file.nextLine();
            Pattern cpochhammer = Pattern.compile("(\\(([^\\)]+)\\)_\\{?([^\\}]+)\\}?)");
            Matcher pochhammer = cpochhammer.matcher(line);
            StringBuffer rplcmntBfr = new StringBuffer();
            while(pochhammer.find())  {
               pochhammer.appendReplacement(rplcmntBfr, "\\\\pochhammer{" + pochhammer.group(2) + "}{" + pochhammer.group(3) + "}");
            }
            pochhammer.appendTail(rplcmntBfr);
            System.out.println(rplcmntBfr);
        }
    }
}

Answer 1

假设:在匹配组的某处，有一个有效的组引用，格式为 "$n"，其中 n 无法匹配原始 中的任何组模式。

因此出现错误:“非法组引用”。

解决方案:使用 "$2" 而不是连接 .group(2) 等

即代替写作:

"\\\\pochhammer{"+ pochhammer.group(2) + "}{" + pochhammer.group(3) + "}"

写:

"\\\\pochhammer{$2}{$3}"

旁注:无需在字符类中转义括号； [^)] 和 [^\)] 一样好用，而且更容易阅读 ;)