oop - Java Callstack with recursion. How to get last Object back?

Question

I want to make a simulator where you can enter rooms and then leave them. If you leave you are in the room before you entered. I want to do it with recursion and call stack. It works good if I go into a new room, but I can't go back. Any solutions for this ?

import java.util.Scanner;

public class Hausaufgabe10Aufgabe01 {

    public static void main(String[] args) {
        Room workingroom = new Room("Arbeitszimmer", false);
        Room bedroom = new Room("Schlafzimmer", false);
        Kitchen kitchen = new Kitchen("Kueche", false, false);
        Bathroom bathroom = new Bathroom("Badezimmer", false, false);
        Room hall = new Room("Flur", false);
        hall.setNeighborRooms(bathroom, kitchen, bedroom, workingroom);
        workingroom.setNeighborRooms(bedroom);
        bedroom.setNeighborRooms(workingroom);
        Flat myFlat = new Flat(bathroom, kitchen, bedroom, workingroom, hall);
        boolean inFlat = false;
        Scanner input = new Scanner(System.in);
        walkThrough(myFlat, hall, input);
    }

    public static void walkThrough(Flat myFlat, Room myRoom, Scanner input) {
        while (true) {

            System.out.println("
Sie sind im: " + myRoom.getName());
            System.out.println("Was wollen sie tun ? ");

            System.out.println("1) Lichtsschalter best?tigen ? ");
            System.out.println("2) Raum verlassen? ");
            System.out.println("3) Nachbar Raum betreten ? ");

            int intMax = 3;
            if (myRoom.getName().equals("Kueche")) {
                System.out.println("4) Herd bet?tigen ? ");
                intMax = 4;
            }
            if (myRoom.getName().equals("Badezimmer")) {
                System.out.println("4) Dusche bet?tigen ? ");
                intMax = 4;
            }

            
            boolean shouldIReturn = false;
            int choosenNumber = input.nextInt();
            switch (choosenNumber) {

            case 1:
                myRoom.useLight();
                break;
            case 2:
                shouldIReturn = true;
                break;
            case 3:
                if (myRoom.getNeighborRooms() != null) {
                    myRoom = chooseRoom(input, myRoom);
                    walkThrough(myFlat, myRoom, input);
                } else {
                    System.out.println("Keine Nachbarraum vorhanden");
                }
                break;
            case 4:
                if (intMax == 4) {
                    myRoom.useSpecial();
                }
                break;
            default:
                System.out.println("
Geben sie eine richtige Eingabe ein!!");
                if(intMax < 4) {
                    System.out.println("1 - 3 
");
                } else {
                    System.out.println("1 - 4 
");
                }
                break;
            }
            
            if (shouldIReturn) {
                return;
            }
        }
    }

    public static Room chooseRoom(Scanner input, Room myRoom) {
        if (myRoom.getNeighborRooms().length > 0) {
            for (int i = 0; i < myRoom.getNeighborRooms().length; ++i) {
                System.out.println((i + 1) + ") "
                        + myRoom.getNeighborRooms()[i].getName());
            }
            int choosenRoom = input.nextInt() - 1;
            return myRoom.getNeighborRooms()[choosenRoom];
        }
        return myRoom.getNeighborRooms()[0];
    }
}

I tried to return so I end the current function and went back to the one before, but I do not get the name of the room I was in before. How can I get the object I was before ?

question from:https://stackoverflow.com/questions/65647853/java-callstack-with-recursion-how-to-get-last-object-back

Answer 1

Make myRoom final and see what compile time error you get.

Think about what was happening before, and you'll realise why you didn't get the original room name when you printed System.out.println(" Sie sind im: " + myRoom.getName());.

In the line myRoom = chooseRoom(input, myRoom); you are setting myRoom to a new value. So you don't have the old value when you return from chooseRoom.