如何实现标识符校验：任意位置含*即无效并允许下划线

Let's tackle this validation problem head-on. Your original code only checks the first character for *, which is why inputs like g*g slip through. We need to adjust the logic to scan the entire identifier and enforce the rules properly.

Key Requirements Recap #

• Reject any identifier that contains * (any position)
• Allow underscores (_) anywhere (start, middle, end)
• Block all other special characters
• First character must be a letter or underscore (aligns with standard identifier conventions)

Step-by-Step Fix #

1. Scan every character for *: As soon as we find one, we can immediately mark the identifier as invalid.
2. Validate the first character: Must be a letter (Character.isLetter()) or underscore.
3. Validate remaining characters: Each one must be a letter, digit (Character.isDigit()), or underscore.

Corrected Complete Code Example #

Here's a full implementation with proper validation logic:

import java.util.Scanner;

public class IdentifierValidator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter an identifier to validate: ");
        String input = scanner.nextLine();
        
        if (isValidIdentifier(input)) {
            System.out.println("Valid identifier!");
        } else {
            System.out.println("Invalid identifier!");
        }
        scanner.close();
    }

    private static boolean isValidIdentifier(String identifier) {
        // Handle empty or null input
        if (identifier == null || identifier.isEmpty()) {
            return false;
        }

        char[] chars = identifier.toCharArray();
        
        // Check each character dynamically
        for (int i = 0; i < chars.length; i++) {
            char c = chars[i];
            
            // Reject immediately if any character is '*'
            if (c == '*') {
                return false;
            }
            
            // Validate first character rule
            if (i == 0) {
                if (!Character.isLetter(c) && c != '_') {
                    return false;
                }
            } 
            // Validate non-first character rules
            else {
                if (!Character.isLetterOrDigit(c) && c != '_') {
                    return false;
                }
            }
        }
        
        // All checks passed
        return true;
    }
}

Test Cases to Verify #

Let's test this with your edge cases and other scenarios:

• Valid: g_g, _test123, MyIdentifier, a_b_c
• Invalid: g*g (contains *), *gg (starts with *), g!g (has exclamation), 123test (starts with digit), g@3 (has @)

This implementation dynamically scans every character, so no matter where * appears, it gets caught. It also properly allows underscores while blocking all other special characters.

内容的提问来源于stack exchange，提问作者ehelp fit