如何检查字符串以数字编号开头？

Question

我有一个包含字母数字字符的字符串.

我需要检查字符串是否以数字开头.

谢谢,

Answer 1

看isDigit(char ch)方法:

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Character.html

并使用该String.charAt()方法将其传递给String的第一个字符.

Character.isDigit(myString.charAt(0));

Answer 2

抱歉,我没有看到你的Java标签,只是在阅读问题.因为我把它们打印出来,所以我会在这里留下我的其他答案.

Java的

String myString = "9Hello World!";
if ( Character.isDigit(myString.charAt(0)) )
{
    System.out.println("String begins with a digit");
}

C++:

string myString = "2Hello World!";

if (isdigit( myString[0]) )
{
    printf("String begins with a digit");
}

正则表达式:

\b[0-9]

一些证明我的正则表达式有效:除非我的测试数据错误？ 替代文字http://i29.tinypic.com/15z5pw8.png

Answer 3

我认为你应该使用正则表达式:

import java.util.regex.*;

public class Test {
  public static void main(String[] args) {
    String neg = "-123abc";
    String pos = "123abc";
    String non = "abc123";
        /* I'm not sure if this regex is too verbose, but it should be
         * clear. It checks that the string starts with either a series
         * of one or more digits... OR a negative sign followed by 1 or
         * more digits. Anything can follow the digits. Update as you need
         * for things that should not follow the digits or for floating
         * point numbers.
         */
    Pattern pattern = Pattern.compile("^(\\d+.*|-\\d+.*)");
    Matcher matcher = pattern.matcher(neg);
    if(matcher.matches()) {
        System.out.println("matches negative number");
    }
    matcher = pattern.matcher(pos);
    if (matcher.matches()) {
        System.out.println("positive matches");
    }
    matcher = pattern.matcher(non);
    if (!matcher.matches()) {
        System.out.println("letters don't match :-)!!!");
    }
  }
}

您可能希望调整此值以接受浮点数,但这将适用于负数.其他答案不适用于否定因为他们只检查第一个字符!更具体地说明您的需求,我可以帮助您调整此方法.

Answer 4

这应该工作:

String s = "123foo";
Character.isDigit(s.charAt(0));

Answer 5

使用正则表达式，例如^\d