一文详解Java正则表达式中的捕获组和反向引用功能

(dog)

((A)(B(C)))

matcher.groupCount();   // 捕获组的总数（不包括 group 0）
matcher.group(0);       // 整个正则匹配到的内容
matcher.group(1);       // 第1个捕获组
matcher.start(1);       // 捕获组1的起始位置
matcher.end(1);         // 捕获组1的结束位置

import java.util.regex.*;

public class CapturingGroupsDemo {
    public static void main(String[] args) {
        String input = "abc123xyz";
        String regex = "(abc)(\\d+)(xyz)";
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(input);

        if (matcher.find()) {
            System.out.println("Group count = " + matcher.groupCount()); 
            System.out.println("Group 0 = " + matcher.group(0)); // abc123xyz
            System.out.println("Group 1 = " + matcher.group(1)); // abc
            System.out.println("Group 2 = " + matcher.group(2)); // 123
            System.out.println("Group 3 = " + matcher.group(3)); // xyz
        }
    }
}

Group count = 3
Group 0 = abc123xyz
Group 1 = abc
Group 2 = 123
Group 3 = xyz

(\d\d)\1

输入：1212   ✅ 匹配
输入：1234   ❌ 不匹配

(\w+)\s\1

输入：hello hello   ✅ 匹配
输入：hello world   ❌ 不匹配

(A(B(C)))

(?:...)

(?:dog|cat){2}