java中的正则表达式[“0-9”]问题
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Regular expression["0-9"] issue in java
提问by Anish
I have a text file as follows:
我有一个文本文件如下：
Title
XYZ
Id name
1 abc
2 pqr
3 xyz
I need to read the content starting with the integer value and I used the regular expression as in the following code.
我需要读取以整数值开头的内容，并使用了以下代码中的正则表达式。
public static void main(String[] args) throws FileNotFoundException {
FileInputStream file= new FileInputStream("C:\Users\ap\Downloads\sample1.txt");
Scanner scanner = new Scanner(file);
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
if (line.startsWith("[0-9]")) {
System.out.println("Line: "+line);
}
}
}
The above code can't detect the lines starting with integers. However, it works fine if single integer values are passed to startsWith()function.
Please suggest, where I went wrong.
上面的代码无法检测以整数开头的行。但是，如果将单个整数值传递给startsWith()函数，它就可以正常工作。请建议，我哪里出错了。
采纳答案by Rohit Jain
String#startsWith(String)method doesn't take regex. It takes a string literal.
String#startsWith(String)方法不使用正则表达式。它需要一个字符串文字。
To check the first character is digit or not, you can get the character at index 0 using String#charAt(int index)method. And then test that character is digit or not using Character#isDigit(char)method:
要检查第一个字符是否为数字，您可以使用String#charAt(int index)方法获取索引 0 处的字符。然后使用Character#isDigit(char)方法测试该字符是否为数字：
if (Character.isDigit(line.charAt(0)) {
System.out.println(line);
}
回答by Fabio
For regex you can use the "matches" method, like this:
对于正则表达式，您可以使用“匹配”方法，如下所示：
line.matches("^[0-9].*")
