Java中如何使用matches方法验证09DD-DDD-DD DD格式的字符串？

Hey there! Let's work through why your current code isn't running correctly and fix it up to validate that "09DD-DDD-DD DD" format properly.

What's Wrong with Your Current Code? #

You've got two key issues here:

• Incorrect regex escaping: In Java, to represent a digit in a regular expression, you need to use \\d (two backslashes). Your code uses //d, which gets treated as literal characters /d instead of matching digits—so the regex can never find a match.
• Mismatched regex structure: Your regex //d{4}-//d{3}-//d{2} //d{2} expects four digits at the start, but you're already checking that the first two characters are "09". This creates a conflict: you're essentially asking for "09" followed by four digits, which doesn't align with your target format of "09DD-DDD-DD DD".

Corrected Code (Recommended Approach) #

The cleanest way to handle this is to let the regex handle the entire validation, including the "09" prefix. This removes redundant checks and ensures the full format is enforced:

public void setPhone(String p) {
    // Regex breakdown:
    // ^ = start of string
    // 09 = matches the required prefix
    // \\d{2} = matches two digits (DD)
    // - = matches the literal hyphen
    // \\d{3} = matches three digits (DDD)
    // - = matches another hyphen
    // \\d{2} = matches two digits (DD)
    //  = matches the space
    // \\d{2} = matches the final two digits (DD)
    // $ = end of string (ensures no extra characters are present)
    if (p != null && p.matches("^09\\d{2}-\\d{3}-\\d{2} \\d{2}$")) {
        this.phone = p;
    } else {
        System.out.println("Phone number must start with 09 and follow the format: 09DD-DDD-DD DD");
    }
}

Alternative (Keeping Your Initial Prefix Check) #

If you want to keep the charAt() check for the "09" prefix, you need to fix the regex and add a length check to avoid StringIndexOutOfBoundsException (if the input string is shorter than 2 characters):

public void setPhone(String p) {
    // First ensure the string is long enough, then check prefix, then validate format
    if (p != null && p.length() == 14 && p.charAt(0) == '0' && p.charAt(1) == '9'
        && p.matches("09\\d{2}-\\d{3}-\\d{2} \\d{2}")) {
        this.phone = p;
    } else {
        System.out.println("Phone number must start with 09 and follow the format: 09DD-DDD-DD DD");
    }
}

Key Notes #

• Always add a null check for the input string p to avoid NullPointerException when calling methods like charAt() or matches().
• The ^ and $ anchors in the regex ensure that the entire string matches the format—no extra characters before or after will be allowed.

内容的提问来源于stack exchange，提问作者Mohadeseh