Java正则表达式错误 - 无组1 [英] Java Regex Error - No group 1

问题描述

我在我的项目中将其作为UnitTest运行

I ran this as a UnitTest in my project

public class RadioTest {

    private static Pattern tier;
    private static Pattern frequency;
    private static Pattern state;

    static {
        tier = Pattern.compile("Tier: \\d");
        frequency = Pattern.compile("Frequency: \\d{3}");
        state = Pattern.compile("State: (OFF|ON)");
    }

    @Test
    public void test() {
        String title = "Tier: 2";
        String title2 = "Frequency: 135";
        String title3 = "State: ON";

        assertTrue(tier.matcher(title).matches());
        assertTrue(frequency.matcher(title2).matches());
        assertTrue(state.matcher(title3).matches());

        Matcher m = tier.matcher(title);

        System.out.println(m.find());
        System.out.println(m.group(1));
    }

}

但是我有一个错误 IndexOutOfBoundsException：没有组1
我知道这与 m.group（1）有关，但是出了什么问题？在控制台中，我也从 m.find（）中看到 true 。我搜索了如何使用正则表达式，但它显示了这样做。

But I got an error IndexOutOfBoundsException: No group 1 I know this has to do with m.group(1), but what's wrong? in the console I also see true from m.find(). I searched how to use regular expressions but it showed to do that.

推荐答案

Pattern.compile("Tier: \\d");

没有定义一个组，所以这个表达式匹配，但是你不能提取一个组。你可能想这样做：

does not define a group so this expression matches but you can't extract a group. You'll probably want to do it like:

Pattern.compile("Tier: (\\d)");

同样适用于您的其他表达式。您需要（）将您要提取的零件包含为组。

Also for your other expressions. You'll need to () enclose parts that you want to extract as group.

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