Pattern.matcher() 究竟是如何工作的？ [复制]

Question

所以我正在尝试创建一个解析器来匹配字符串的某些部分。字符串看起来像 f(q[group1],[group2])=(q[group3],[group4],[group5])。下面代码中的 Pattern.matches() 返回 true，但我无法通过 matcher.group(int) 访问组。提供的代码中的最后一行抛出：java.lang.IllegalStateException: No match available

public class Parser {
   Pattern pattern;
   Matcher matcher;
   String g;

public Parser(String s) {
   g = s.replaceAll("\\s+", "");
   pattern = Pattern.compile("^f\\(q(\\d+),(.)\\)=\\(q([+-]*\\d+),(.),([+-])1\\)$");
   matcher = pattern.matcher(g);
   boolean b = Pattern.matches("^f\\(q(\\d+),(.)\\)=\\(q([+-]*\\d+),(.),([+-])1\\)$",g);

 System.out.println(b +   " ");
 System.out.println(matcher.group(1));
}
}

Answer 1

你永远不会匹配任何与 matcher 匹配的东西。我不确定你为什么要调用静态方法 Pattern.matches 但那行应该是

boolean b = matcher.matches();

像这样：

public class Parser {
    Pattern pattern;
    Matcher matcher;
    String g;

    public Parser(String s) {
        g = s.replaceAll("\\s+", "");
        pattern = Pattern.compile("^f\\(q(\\d+),(.)\\)=\\(q([+-]*\\d+),(.),([+-])1\\)$");
        matcher = pattern.matcher(g);
        boolean b = matcher.matches();

        System.out.println(b + " ");
        System.out.println(matcher.group(1));
    }
}