Java Regex匹配组错误？

Question

我使用swing组件编写了一个基本的CLI,并使用Regex来识别命令.

我遇到过一些特殊的事情,我无法解释.我在这做错了什么？

这是我的代码:

class GraphCommandFactory {

private final GraphSearchController controller;
private final GraphSearchModel model;
private final ArrayList<Pattern> commands;

public GraphCommandFactory(GraphSearchController controller, GraphSearchModel model) {
    this.model = model;
    this.controller = controller;
    this.commands = new ArrayList<>();

    commands.add(Pattern.compile("SET START ([A-Z]{4,8})"));
}

public Command createCommand(String commandString) {
    Command returnCommand;

    // Test the string against each regex
    int command = 0;
    Matcher matcher = commands.get(command).matcher(commandString);
    ...

private String[] extractArguments(Matcher matcher) {
    String[] arguments = new String[matcher.groupCount()];

    for (int i = 0, j = matcher.groupCount(); i < j; i++) {
        arguments[i] = matcher.group(i);
    }

    return arguments;
}

extractArguments函数附带问题...使用模式(在Matcher中):

Pattern.compile("SET START ([A-Z]{4,8})"));

输掉了最后一组.但是,如果我将其修改为:

Pattern.compile("SET START ([A-Z]{4,8})()"));

然后它正确捕捉我想要的东西.

我是否误解了如何使用正则表达式,模式和匹配器？或者这是最后一个捕获组丢失的错误？

我使用Java SDK 1.8和Netbeans作为我的IDE.使用调试工具让我更加聪明.

Answer 1

问题出在你的for循环中:

for (int i = 0, j = matcher.groupCount(); i < j; i++) {
    arguments[i] = matcher.group(i);
}

因为你只是循环比1少 matcher.groupCount

将其更改为:

for (int i = 0; i <= matcher.groupCount(); i++) {
    arguments[i] = matcher.group(i);
}

根据Javadoc:

groupCount返回此匹配器模式中的捕获组数.组0表示按惯例的整个模式.它不包含在此计数中.