Java Cant put object into hashmap connected to other object

[Java] Cant put object into hashmap connected to other object - Printable Version

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+---- Thread: [Java] Cant put object into hashmap connected to other object (/showthread.php?tid=5927877)

Cant put object into hashmap connected to other object - deadsh0t - Jan 9, 2019

So im making this consolebased game for my software development class as my assessment
But i cant understand this bit or why it is wrong to do it like this.

So basicly i have 10 rooms
so a room has the following things:
-A roomnumber
-A hashmap that contains a Room as value and a String as key
-An arraylist for items (Item has its own class ofcourse)

Now the problem, A room can be exited from 4 direction North,East,South,West so thats the String/key in the hashmap
It can also have 2 exits or 1 or 3.
So in that hashmap i save the direction as key and as value another room object so i can keep track wich exit goes to wich room.
so i have a method for adding exits. that looks like this:

Code 
public class Room {

    private int RoomNo;

    private HashMap<String, Room> Exits;

    public Room(int roomNo){

        Exits = new HashMap<String, Room>();

        this.RoomNo = roomNo;

    }

    public void Addexits(Room room, String exitDirection){

            Exits.put(exitDirection,room);

    }

And than in the game class i create 10 rooms and use call the addexits method to add exits that looks like this:

Code 
Rooms = new ArrayList<Room>();

     //initialize all rooms

     room1 = new Room(1);

     room1.Addexits(room4,"West");

     room1.Addexits(room3,"East");

     room2 = new Room(2);

     room2.Addexits(room2,"North");

     room2.Addexits(room2,"South");

     room3 = new Room(3);

     room3.Addexits(room3,"West");

     room3.Addexits(room3,"East");

     room4 = new Room(4);

     room4.Addexits(room4,"West");

     room4.Addexits(room4,"East");

However as you can see with room1 i try to add 2 exits 1 in the west to room4 and 1 in the east to room3 however when i run this it shows this in the hashmap:
West -> null
East -> null

But when i add 2 exits both with object room1 it puts it like it should be like this:

West -> room1
East -> room1

So i dont really get what im doing wrong each room has its own hashmap on creation and the rooms are already created so that shouldnt be an issue.

RE: Cant put object into hashmap connected to other object - GenericSkid - Jan 10, 2019

Your rooms are null when you add them... initialize all the rooms first THEN add them as exits.

UpperCaseVariables is a bad convention in Java for field and variable names. Using camalCaseStyle is the typical convention.
You can make your fields final by adding it as a modifier.
Instead of instantiating exits in the constructor it can be done in-line.
The instantiation of exits can remove redundant genrics: new HashMap<>();
The definition of exits can be made clearer by changing the field type to Map. This won't affect the instantiation / value. It takes less space, and is more abstract.

PHP Code 


<?php 
public class Room {
    private final int roomNo;
    private final Map<String, Room> exits new HashMap<>();

    public Room(int roomNo) {
        this.roomNo = roomNo;
    }

    public void addExit(Room room, String direction){
            exits.put(direction, room);
    } 

RE: Cant put object into hashmap connected to other object - deadsh0t - Jan 10, 2019

(Jan 10, 2019 03:37 AM)GenericSkid Wrote: Your rooms are null when you add them... initialize all the rooms first THEN add them as exits.

UpperCaseVariables is a bad convention in Java for field and variable names. Using camalCaseStyle is the typical convention.

You can make your fields final by adding it as a modifier.

Instead of instantiating exits in the constructor it can be done in-line.

The instantiation of exits can remove redundant genrics: new HashMap<>();

The definition of exits can be made clearer by changing the field type to Map. This won't affect the instantiation / value. It takes less space, and is more abstract.

PHP Code
<?php public class Room { private final int roomNo; private final Map<String, Room> exits new HashMap<>(); public Room(int roomNo) { this.roomNo = roomNo; } public void addExit(Room room, String direction){ exits.put(direction, room); }

Yeah i figured it out i felt so dumb haha
Yeah the camalCaseStyle is something that is a must in my assingment i really need to stick to it,but sometimes i forget to use it.
Thanks for the tip on the map and making it final :)