Store hashMap in array

Question

I would like to store HashMaps in an array. I'm trying to make just one HashMap, fill it with specific information and store it into one element of an array. Then I would like to overwrite the information in that Hashmap with different information and then store that into a different element of that array. I would like to do this multiple times. What's the best way to go about doing this?

Right now I have:

HashMap[][] location = new HashMap[columns][rows];
HashMap <String, String> area = new HashMap <String, String> ();

public Map() {

    area.put("description", "You are in the upper left\n");
    location[0][0] = area;

    area.put("description", "You are in the upper middle\n");
    location[1][0] = area;
}

The problem with this is that now both location[0][0] and location[1][0] have the same description.

You should use Map for area instead of HashMap. It's a good practice in the sense that it'll be easier to change implementation in future. — Arham
– Arham, Commented Oct 18, 2012 at 18:45
I'm not sure if my area and your area are the same. I'm using area in terms of a location on a map, not mathematically. Is using a HashMap better in my case? — tazboy
– tazboy, Commented Oct 18, 2012 at 19:35
You are confusing the literal meaning of Map with the Map interface of Java. I meant you should initialize your area variable as, Map<String, String> area = new HashMap <String, String>(); This would help you in future when you want to shift to let say LinkedHashMap, Treemap or any other flavor of Map. — Arham
– Arham, Commented Oct 18, 2012 at 19:42
I didn't think of that. In fact, I didn't know those other ones even existed. Thanks. — tazboy
– tazboy, Commented Oct 18, 2012 at 20:18
Then I suggest you take a look at them and figure out the benefactions over one another. It's always good to have a reason before choosing a data structure. :) — Arham
– Arham, Commented Oct 18, 2012 at 20:23

John B · Accepted Answer · 2012-10-18 18:22:52Z

2

location[0][0] and location[1][0] hold the same pointer to area

you should do like this

location[0][0] = createArea("You are in the upper left\n");
location[1][0] = createArea("You are in the upper middle\n");



HashMap <String, String> createArea(String desc){
    HashMap <String, String> area = new HashMap <String, String> ();
    area.put("description", desc);
    return area;
}

edited Oct 18, 2012 at 18:22

John B

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answered Oct 18, 2012 at 18:21

farmer1992

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1 Comment

tazboy Over a year ago

That did it! Thanks. I like how simple it is. I knew I needed to make a new HashMap but I couldn't picture what the code would look like. Methods are key.

John B · Accepted Answer · 2012-10-18 18:20:52Z

0

You need to create a different instance of the Map to be stored in each location.

 public Map() {      

   Map<String, String> area = new HashMap<String, String>();
   area.put("description", "You are in the upper left\n");     
   location[0][0] = area;      

   area = new HashMap<String, String>();
   area.put("description", "You are in the upper middle\n");    
   location[1][0] = area; }

answered Oct 18, 2012 at 18:20

John B

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