Sample Java code formatting a Brazilian phone number using regex along with String.replaceAll()

PhoneNumberFormat.java

class PhoneNumberFormat {
    public static void main (String[] args) {
        System.out.println("21436587".replaceAll("^([0-9]{4,5})[^0-9]*([0-9]{4})$", "$1-$2"));   // outputs "2143-6587"
        System.out.println("2143-6587".replaceAll("^([0-9]{4,5})[^0-9]*([0-9]{4})$", "$1-$2"));  // outputs "2143-6587"
        
        System.out.println("921436587".replaceAll("^([0-9]{4,5})[^0-9]*([0-9]{4})$", "$1-$2"));  // outputs "92143-6587"
        System.out.println("92143-6587".replaceAll("^([0-9]{4,5})[^0-9]*([0-9]{4})$", "$1-$2")); // outputs "92143-6587"
    }
}