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Question about the task

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First of all, I have already passed the task so I can't really post my whole code. So I'm just posting original code for your reference.

public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        Person person = null;
        String key;
        while (!(key = reader.readLine()).equals("exit")) {
            if ("player".equals(key)) {
                person = new Player();
            } else if ("dancer".equals(key)) {
                person = new Dancer();
            }
            haveFun(person);
        }
    }

    public static void haveFun(Person person) {
        //write your code here
    }

    interface Person {
    }

    static class Player implements Person {
        void play() {
            System.out.println("playing");
        }
    }

    static class Dancer implements Person {
        void dance() {
            System.out.println("dancing");
        }
    }
}

The strange thing is that if I type other than player or dancer - like "hello", it always displays dancing. Could anyone explain why it's happening and how to prevent it?

Comments (3)

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Juan Patino

Level 15 , Atlanta, United States

18 December 2020, 20:01

It's actually because of the while loop in the code. If the key is not equal to "player" or "dancing" then it will maintain the previous reference of the object (in your case "dancing"). Try inputting something besides player or dancing on your first line of input and you will get the expected output. This is because on the first line of input, person is null. You are assigning a reference to it with the key string.

Zserbo

Level 22 , Budapest, Hungary

19 May 2020, 20:37

I was about to type the same thing as AnnemiekFF. You probably used an if-else statement which checks if a person is an instance of Player, and if not, it calls the Dancer.dance() method. This is my haveFun method and it works as intended:

public static void haveFun(Person person) {
        if (person instanceof Player) {
            Player player = (Player) person;
            player.play();
        }
        else if (person instanceof Dancer) {
            Dancer dancer = (Dancer) person;
            dancer.dance();
        }
    }

AnnemiekFF

Level 41 , Breda, Netherlands

19 May 2020, 08:00

That will probably be an error in your HaveFun method. You should check if person is an instance of dancer or an instance of player. do not use if, else. But if, if or if, else if