Java 正则表达式中的反向引用
java programming java8object oriented programming
捕获组是一种将多个字符视为单个单元的方法。它们是通过将要分组的字符放在一组括号内来创建的。例如，正则表达式 (dog) 创建一个包含字母"d"、"o"和"g"的组。
捕获组的编号是通过从左到右计算其左括号来计算的。例如，在表达式 ((A)(B(C))) 中，有四个这样的组 -
((A)(B(C))) (A) (B(C)) (C)
示例
反向引用允许使用数字(如 \#，其中 # 是组号)重复捕获组。请参阅以下示例:
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Tester {
public static void main(String[] args) {
//2 followed by 2 five times
String test = "222222";
String pattern = "(\d\d\d\d\d)";
Pattern r = Pattern.compile(pattern);
Matcher m = r.matcher(test);
if (m.find( )) {
System.out.println("Matched!");
}else{
System.out.println("not matched!");
}
//\1 as back reference to capturing group (\d)
pattern = "(\d)\1{5}";
r = Pattern.compile(pattern);
m = r.matcher(test);
if (m.find( )) {
System.out.println("Matched!");
}else{
System.out.println("not matched!");
}
}
}
