Java program problem: Unexpected value num

June 14, 2023

public class Demo {
    public static void main(String args[]) {
        char c = 'A' ;
        int num = 10 ;

        switch(c) {
            case 'B' :
                num++ ;
            case 'A' :
                num++ ;
            case 'Y' :
                num++ ;
                break ;
            default :
                num-- ;
        }

        System.out.println(num);
    }
}

I think the program will passed case 'A' so the num will be 11.
I ran it in Idea and saw that the program passed case 'A' and case 'Y'(???). Finally, the num is 12.

I try this:
System.out.println('A' == 'Y');
and it returnfalse

>Solution :

In the example the program first passes case 'A' since the char in c is A, but then it "falls through" to case 'Y' since case 'A' does not end with a break.

If this behaviour is not desired, add a break to case 'A'.

Read https://medium.com/swlh/understanding-switch-case-fall-through-in-java-70b448427b0a for more details.