initialization of variables

[Tiam Bezalel]

hi,
why do i have "nullB" as output? i was expecting "XB" as output. please explain.

    class Message {
        String msg = "X"; //Line n1
        
        Message() {
            Message(); //Line n2
        }
        
        void Message() { //Line n3
            System.out.println(msg += "A"); //Line n4
        }
    }
     
    class MyMessage extends Message {
        String msg = "Y"; //Line n5
        
        MyMessage() {} //Line n6
        
        void Message() { //Line n7
            System.out.println(msg += "B"); //Line n8
        }
    }
     
    public class Test {
        public static void main(String[] args) {
            new MyMessage(); //Line n9
        }
    }

thanks.

[Stephan van Hulst]

This is the order of operations:

n9: new MyMessage();
n1: Message.msg = "X";
n2: Message();
n8: System.out.println(MyMessage.msg += "B");
n5: MyMessage.msg = "Y";
n6: Empty constructor body

For clarity, I qualified msg to clearly distinguish between Message.msg and MyMessage.msg, which are two different variables.

As you can see, Line n8 is executed before line n5, meaning that before "B" is appended to MyMessage.msg, it still has its default value of null.