java - OCP 7 II正则表达式

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Regular expression - Greedy quantifier [duplicate]
                                
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import java.util.regex.*;

public class Regex2 {

    public static void main(String[] args) {
        Pattern p = Pattern.compile("\\d*");
        Matcher m = p.matcher("ab34ef");
        boolean b = false;
        while ( m.find()) {
            System.out.print(m.start() + m.group());
        }
    }
}

为什么此代码产生输出：01234456

最佳答案

@vks是正确的：
如果您使用的是\\d*，则适用于每个字符：

Index: char = matching:
    0: 'a'  = "" because no integer
    1: 'b'  = "" because no integer
    2: '3'  = "34" because there is two integer between index [2-3]
       '4'    is not checked because the index has been incremented in previous check.
    4: 'e'  = ""
    5: 'f'  = "" because no integer
    6: ''   = "" IDK

它产生0，“”，1，“”，2，“ 34”，4，“”，5，“”，6，“” = 01234456（这就是为什么得到它）。

如果使用\\d+，则只有具有一个或多个整数的组将匹配。