String Array Values and HashMaps

Question

I've been trying to make a maze type of game by reading in from a configuration file using HashMaps to distinguish between a Room attribute vs Door Attribute. If I just print the String[] values they print the corresponding config values, however, when I try to print the values using a HashMap by calling it by its key, it tells me that the values are null. Any advice?

My code:

     while (file.hasNextLine()) {
            String line = file.nextLine();
            if (line.isEmpty()) {
              continue;
            }
            Scanner scanner = new Scanner(line);
            String type = scanner.hasNext() ? scanner.next() : "";

            String name = scanner.hasNext() ? scanner.next() : "";

            String wall1 = scanner.hasNext() ? scanner.next() : "";

            String wall2 = scanner.hasNext() ? scanner.next() : "";

            String wall3 = scanner.hasNext() ? scanner.next() : "";

            String wall4 = scanner.hasNext() ? scanner.next() : "";

            HashMap<String,String[]> roomSite = new HashMap<String, String[]>();
            HashMap<String,String[]> doorSite = new HashMap<String, String[]>();

            String[] options = new String[]{wall1,wall2,wall3,wall4};

            if(type.equals("room")){
                roomSite.put(name, options);
            }else if(type.equals("door")){
                doorSite.put(name, options);
            }else{
                System.out.println("Error in config file. Please check that all options are valid.");
            }
            System.out.println(roomSite.get(0));
            System.out.println(doorSite.get("d0"));
  }

Output:

null
null
null
null
null
null
null
[Ljava.lang.String;@e9e54c2
null
null

config.ini

room 0 wall d0 wall wall
room 1 d0 wall d1 wall
room 2 wall wall wall d1
door d0 0 1 close
door d1 1 2 open

Well, do you have 0 as a key in roomSite or "d0" as a key in doorSite on the iterations when it prints null? — Oliver Charlesworth
– Oliver Charlesworth, Commented Nov 9, 2015 at 21:54
It might make more sense if you use String.split() on your line instead of all those scanners. — OneCricketeer
– OneCricketeer, Commented Nov 9, 2015 at 21:56

Evan LaHurd · Accepted Answer · 2015-11-09 22:01:50Z

1

You have System.out.println(roomSite.get(0)); when it should be System.out.println(roomSite.get("0"));

Your maps map from String to String[], not Integer to String[].

Also, if you want to get a more meaningful print statement instead of [Ljava.lang.String;@e9e54c2, you can use the Arrays.toString() method.

edited Nov 9, 2015 at 22:01

answered Nov 9, 2015 at 21:56

Evan LaHurd

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4 Comments

adventuredoge Over a year ago

Hi, after making the key "0", now it gives me: [Ljava.lang.String;@e9e54c2 followed by nulls, is that normal?

Evan LaHurd Over a year ago

You should initialize your maps before you start reading from your file. Each time you're reading in a line, you're creating a new HashMap. So on the first iteration when you read in room 0, you add its details to the map, which is why you see the [Ljava.lang.String;@e9e54c2 printed. Afterwards, you're creating new maps, and adding the other rooms/doors. The "0" details aren't in the new maps, so you only see null printed on the subsequent iterations.

adventuredoge Over a year ago

Ooooh, ok. It works now. Thanks very much for the help! I was stuck on that for like 2 hrs now :)

Evan LaHurd Over a year ago

No problem, glad to help!

gonzo · Accepted Answer · 2015-11-09 22:07:30Z

Initialize your HashMaps before iterating through your file. Try something like this:

public static void main(String []argh) throws FileNotFoundException
{
    Scanner scan = new Scanner(new File("config.ini"));
    HashMap<String, String[]> roomSite = new HashMap<>();
    HashMap<String, String[]> doorSite = new HashMap<>();
    while(scan.hasNext()){
        String type = scan.next();
        String name = scan.next();
        String[] walls = scan.nextLine().trim().split(" ");
        switch(type){
        case "room":
            roomSite.put(name, walls);
            break;
        case "door":
            doorSite.put(name,  walls);
            break;
        default:
            System.out.println("Error in config file. Please check that all options are valid.");
        }
    }
    System.out.println(Arrays.toString(roomSite.get("0")));
    System.out.println(Arrays.toString(doorSite.get("d0")));
}

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