Matcher.find（）的工作原理 [英] How Matcher.find() works

问题描述

我正在测试一个Matcher和Pattern类的小存根...请看下面的小存根..

I am testing a small stub of Matcher and Pattern class...see the following small stub..

package scjp2.escape.sequence.examples;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Sample_19 {

    public static void main(String a[]){
        String stream = "ab34ef";
        Pattern pattern = Pattern.compile("\\d*");

        //HERE * IS GREEDY QUANTIFIER THAT LOOKS FOR ZERO TO MANY COMBINATION THAT 
        //START WITH NUMBER 
        Matcher matcher = pattern.matcher(stream);

        while(matcher.find()){
            System.out.print(matcher.start()+matcher.group());
        }
    }

}

此处。我们比较的字符串是ab34ef。长度为6。

Here ...our string which we are comparing is "ab34ef". which is of length 6.

Noe让我们看看迭代......

Noe let see the iteration...

1 0

2 1

3 2 34

4 4

5 5

现在..let结合... matcher.start（）+ matcher.group（）....
我们计算的输出是：0123445

Now ..let combine...matcher.start() + matcher.group().... the output as per our calculation is : 0123445

但是，存根生成01234456。

But, the stub generates 01234456.

I我无法理解6的来源。
字符串索引从零开始，所以这里可以有最大索引是5.So从哪里开始？

I am not able to understand from where the "6" is coming. String index starts from zero and so here there can be maximum index is 5.So from where 6 is coming??

它迭代循环六次..怎么样 ？
有什么建议吗？

It iterates over the loop six times..How ? Any suggestion ?

推荐答案

你的正则表达式可以匹配零个字符。最后一个匹配是在字符串末尾出现的零宽度字符串，在索引5处的字符之后。因此，此零宽度字符串的索引为6.

Your regular expression can match zero characters. The final match is a zero width string occurring at the end of the string, after the character at index 5. The index of this zero width string is therefore 6.

另外，如果使用分隔符使输出更具可读性，您可能还会发现更容易理解发生了什么：

As an aside, you might also find it easier to understand what is going on if you use separators to make the output more readable:

System.out.println(matcher.start()+ ": " + matcher.group());

结果：

0: 
1: 
2: 34
4: 
5: 
6: 

ideone

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