这应该给予你一个起点。

public class EmailObfuscator {

    public static void main(String[] args) {
        String email = "firstname@gmail.com";
        String obfuscatedEmail = obfuscateEmail(email);
        System.out.println(obfuscatedEmail);
    }

    public static String obfuscateEmail(String email) {
        int atIndex = email.indexOf("@");
        if (atIndex > 4) {
            String firstPart = email.substring(0, 2);
            String lastPart = email.substring(atIndex - 2);
            StringBuilder obfuscatedPart = new StringBuilder();
            for (int i = 2; i < atIndex - 2; i++) {
                obfuscatedPart.append("*");
            }
            return firstPart + obfuscatedPart + lastPart;
        } else {
            // Email address is too short decide what to do
            return email;
        }
    }
}

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