does default case MUST be included in switch statements in Java

Question

I was just wondering if default case MUST be included in switch statements in Java. I understand it is good practice to include default cases. The reason why I ask is because for the code below, if I delete default case, the code will provide error. Could someone please help me clarify the concept? Thanks in advance for any help!

public class SwitchDemo {
    public static void main(String[] args) {

        int month = 8;
        String monthString;
        switch (month) {
            case 1:  monthString = "January";
                     break;
            case 2:  monthString = "February";
                     break;
            case 3:  monthString = "March";
                     break;
            case 4:  monthString = "April";
                     break;
            case 5:  monthString = "May";
                     break;
            case 6:  monthString = "June";
                     break;
            case 7:  monthString = "July";
                     break;
            case 8:  monthString = "August";
                     break;
            case 9:  monthString = "September";
                     break;
            case 10: monthString = "October";
                     break;
            case 11: monthString = "November";
                     break;
            case 12: monthString = "December";
                     break;
            default: monthString = "Invalid month"; //if delete will produce error
                     break;
        }
        System.out.println(monthString);
    }
}

Answer 1

While the default clause is not mandatory, if you remove it, monthString may not be initialized, so you get a compilation error when you attempt to print it with System.out.println(monthString);.

You can remove the default clause if you give monthString a default value when you declare it. For example :

String monthString = "Invalid month";

This will give the same behavior as your current switch statement, which includes the default clause.