public static void main(String[] args) {
String str = "请完善你的电子签名\xF0\x9F\x91\x8C";
String str2 = str.replaceAll("\\x[A-Z,0-9][A-Z,0-9]", "?");
System.out.println(str2);
}

public static void main(String[] args) {
String str = "请完善你的电子签名\xF0\x9F\x91\x8C";
String str2 = str.replaceAll("\\x[A-Z,0-9][A-Z,0-9]", "?");
System.out.println(str2);
}