也可以使用编号获取相应值。

public static final String P_NAMED = "(?<year>d{4})-(?<md>(?<month>d{2})-(?<date>d{2}))";public static final String DATE_STRING = "2017-04-25"; Pattern pattern = Pattern.compile(P_NAMED);Matcher matcher = pattern.matcher(DATE_STRING);matcher.find();System.out.printf(" ===========使用名称获取=============");System.out.printf(" matcher.group(0) value:%s", matcher.group(0));System.out.printf(" matcher.group('year') value:%s", matcher.group("year"));System.out.printf(" matcher.group('md') value:%s", matcher.group("md"));System.out.printf(" matcher.group('month') value:%s", matcher.group("month"));System.out.printf(" matcher.group('date') value:%s", matcher.group("date"));matcher.reset();System.out.printf(" ===========使用编号获取=============");matcher.find();System.out.printf(" matcher.group(0) value:%s", matcher.group(0));System.out.printf(" matcher.group(1) value:%s", matcher.group(1));System.out.printf(" matcher.group(2) value:%s", matcher.group(2));System.out.printf(" matcher.group(3) value:%s", matcher.group(3));System.out.printf(" matcher.group(4) value:%s", matcher.group(4));

PS:非捕获组

在左括号后紧跟 ?:，而后再加上正则表达式，构成非捕获组 (?:Expression)。

对于时间字符串：2017-04-25，表达式如下:

(?:d{4})-((d{2})-(d{2}))

这个正则表达式虽然有四个左括号，理论上有 4 个捕获组。但是第一组 (?:d{4})，其实是被忽略的。当使用 matcher.group(4) 时，系统会报错。

编号捕获组匹配
0(d{4})-((d{2})-(d{2}))2017-04-25
1((d{2})-(d{2}))04-25
2(d{2})04
3(d{2})25
public static final String P_UNCAP = "(?:d{4})-((d{2})-(d{2}))";public static final String DATE_STRING = "2017-04-25"; Pattern pattern = Pattern.compile(P_UNCAP);Matcher matcher = pattern.matcher(DATE_STRING);matcher.find();System.out.printf(" matcher.group(0) value:%s", matcher.group(0));System.out.printf(" matcher.group(1) value:%s", matcher.group(1));System.out.printf(" matcher.group(2) value:%s", matcher.group(2));System.out.printf(" matcher.group(3) value:%s", matcher.group(3)); // Exception in thread "main" java.lang.IndexOutOfBoundsException: No group 4System.out.printf(" matcher.group(4) value:%s", matcher.group(4));

总结

  • 普通捕获组使用方便；

  • 命名捕获组使用清晰；

  • 非捕获组目前在项目中还没有用武之地。

原文地址：https://blog.csdn.net/just4you/article/details/70767928