如何验证字符串为有效的USSD码？求正确的Java正则表达式

Let's work through this USSD regex problem together. First, let's restate your requirements clearly to make sure we cover every base:

• Must start with *
• Can include digits (0-9) or single * characters (no consecutive ** allowed)
• Must end with exactly one # (no other # characters anywhere in the string)

The Correct Regex Pattern #

Here's the regex that satisfies all your rules:

public static final Pattern USSD = Pattern.compile("^\\*(?:\\d|\\*(?!\\*))*#$");

Breaking Down the Regex #

Let's unpack each part so you understand how it works:

• ^\\*: Ensures the string starts with a single * (we escape * because it’s a special character in regex)
• (?:\\d|\\*(?!\\*))*: A non-capturing group that matches any number of valid middle characters:
  • \\d: Matches any digit from 0-9
  • \\*(?!\\*): Matches a single * only if there isn’t another * right after it (this stops consecutive ** from being allowed)
  • The trailing * means this group can repeat zero or more times (so even a simple *# counts as valid)
• #$: Ensures the string ends with exactly one #, and since we’re using ^ (start) and $ (end) anchors, there’s no space for extra # characters anywhere else.

Test Cases #

Let’s verify with your examples plus some edge cases to confirm it works:

public class UssdValidationTest {
    public static final Pattern USSD = Pattern.compile("^\\*(?:\\d|\\*(?!\\*))*#$");

    public static void main(String[] args) {
        // Valid scenarios
        System.out.println(USSD.matcher("*123#").matches()); // true
        System.out.println(USSD.matcher("*1*2*3#").matches()); // true
        System.out.println(USSD.matcher("*#").matches()); // true
        System.out.println(USSD.matcher("*987*65*4321#").matches()); // true

        // Invalid scenarios
        System.out.println(USSD.matcher("**123#").matches()); // false (consecutive *)
        System.out.println(USSD.matcher("*123##").matches()); // false (extra #)
        System.out.println(USSD.matcher("123#").matches()); // false (doesn't start with *)
        System.out.println(USSD.matcher("*123").matches()); // false (doesn't end with #)
        System.out.println(USSD.matcher("*1**2#").matches()); // false (consecutive *)
    }
}

This regex should handle all your use cases perfectly. If you need to adjust for any edge cases we didn't cover, just let me know!

内容的提问来源于stack exchange，提问作者GV_FiQst