java - 正则表达式示例

Question

我有点看不懂这个例子。。。我不明白这个字符串模式写的是什么。另外，什么是find？我正在从 TutorialsPoint 学习这个。

拜托，谁能帮我理解一下？

代码:

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

public class RegexMatches {
    public static void main(String args[]) {

        // String to be scanned to find the pattern.
        String line = "This order was placed for QT3000! OK?";
        String pattern = "(.*)(\\d+)(.*)";

        // Create a Pattern object
        Pattern r = Pattern.compile(pattern);

        // Now create matcher object.
        Matcher m = r.matcher(line);
        if (m.find()) {
            System.out.println("Found value: " + m.group(0));
            System.out.println("Found value: " + m.group(1));
            System.out.println("Found value: " + m.group(2));
        } else {
            System.out.println("NO MATCH");
        }
    }
}

输出:

Found value: This order was placed for QT3000! OK?
Found value: This order was placed for QT300
Found value: 0

Answer 1

该模式有 3 个捕获组

• (.*) 表示零个或多个任意字符(捕获组 1)
• (\\d+)表示一个或多个数字(捕获组2)
• (.*) 表示零个或多个任意字符(捕获组 3)

当 find() 被调用时，它“尝试找到与模式匹配的输入序列的下一个子序列。” ( Matcher.Find() )

当您调用这些行时:

System.out.println("Found value: " + m.group(0));
System.out.println("Found value: " + m.group(1));
System.out.println("Found value: " + m.group(2));

• m.group(0) 表示正则表达式计算的整个字符串
• m.group(1) 指捕获组1(任意字符的零个或多个)
• m.group(2) 指捕获组2(一位或多位)
• 您目前没有输出捕获组 3(零个或多个任意字符)

您会看到 m.group(1) 返回了 This order was placed for QT300 并且最后一个零留在了 m.group( 2) 因为捕获组 2 必须至少有 1 个数字。

如果您要将捕获组 3 (m.group(3)) 添加到输出，它将显示 m.group(2)< 的最后一个零之后的剩余字符串.

换句话说:

System.out.println("Found value: " + m.group(0));
System.out.println("Found value: " + m.group(1));
System.out.println("Found value: " + m.group(2));
System.out.println("Found value: " + m.group(3));

会显示:

Found value: This order was placed for QT3000! OK?
Found value: This order was placed for QT300
Found value: 0
Found value: ! OK?

希望这对您有所帮助!