2D Array with variable size

Question

What I'm trying to accomplish is have something like

String[][] array = new String[sizeX][sizeY]

SizeX would be based on the length of a root JSON array, and sizeY based on the length of an array inside the root JSON array.

Thinking about it, I could use a single array of arrays, but I'm not sure how I'd reference the internal array to get information back from it. For example:

String[] array = new String[sizeX]; 
array[i] = new String[sizeY]; // initialized to variable size of JSON

From here, how would I reference the internal array the objects in the internal array?

The JSON

{"23591778": {
   "pages": [
      {
         "masteries": [
            {
               "id": 4211,
               "rank": 2
            },
            {
               "id": 4214,
               "rank": 2
            },
            {
               "id": 4134,
               "rank": 3
            },
            {
               "id": 4124,
               "rank": 1
            },
            {
               "id": 4114,
               "rank": 1
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4112,
               "rank": 4
            },
            {
               "id": 4221,
               "rank": 1
            },
            {
               "id": 4144,
               "rank": 1
            },
            {
               "id": 4122,
               "rank": 3
            },
            {
               "id": 4152,
               "rank": 3
            },
            {
               "id": 4141,
               "rank": 1
            },
            {
               "id": 4111,
               "rank": 1
            },
            {
               "id": 4132,
               "rank": 1
            },
            {
               "id": 4232,
               "rank": 1
            },
            {
               "id": 4162,
               "rank": 1
            },
            {
               "id": 4131,
               "rank": 1
            }
         ],
         "id": 34787712,
         "name": "Blind",
         "current": false
      },
      {
         "masteries": [
            {
               "id": 4212,
               "rank": 2
            },
            {
               "id": 4233,
               "rank": 3
            },
            {
               "id": 4242,
               "rank": 1
            },
            {
               "id": 4214,
               "rank": 2
            },
            {
               "id": 4114,
               "rank": 1
            },
            {
               "id": 4251,
               "rank": 1
            },
            {
               "id": 4112,
               "rank": 4
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4122,
               "rank": 3
            },
            {
               "id": 4262,
               "rank": 1
            },
            {
               "id": 4224,
               "rank": 1
            },
            {
               "id": 4252,
               "rank": 3
            },
            {
               "id": 4132,
               "rank": 1
            },
            {
               "id": 4241,
               "rank": 3
            },
            {
               "id": 4232,
               "rank": 1
            }
         ],
         "id": 34787713,
         "name": "AD/Tank Jungle",
         "current": false
      },
      {
         "masteries": [
            {
               "id": 4242,
               "rank": 1
            },
            {
               "id": 4233,
               "rank": 3
            },
            {
               "id": 4243,
               "rank": 1
            },
            {
               "id": 4211,
               "rank": 2
            },
            {
               "id": 4214,
               "rank": 2
            },
            {
               "id": 4213,
               "rank": 2
            },
            {
               "id": 4114,
               "rank": 1
            },
            {
               "id": 4252,
               "rank": 2
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4113,
               "rank": 4
            },
            {
               "id": 4221,
               "rank": 1
            },
            {
               "id": 4123,
               "rank": 3
            },
            {
               "id": 4262,
               "rank": 1
            },
            {
               "id": 4224,
               "rank": 1
            },
            {
               "id": 4133,
               "rank": 1
            },
            {
               "id": 4234,
               "rank": 1
            },
            {
               "id": 4232,
               "rank": 1
            }
         ],
         "id": 34787714,
         "name": "Mumu",
         "current": true
      },
      {
         "masteries": [
            {
               "id": 4211,
               "rank": 2
            },
            {
               "id": 4121,
               "rank": 1
            },
            {
               "id": 4214,
               "rank": 2
            },
            {
               "id": 4134,
               "rank": 3
            },
            {
               "id": 4114,
               "rank": 1
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4112,
               "rank": 4
            },
            {
               "id": 4144,
               "rank": 1
            },
            {
               "id": 4221,
               "rank": 1
            },
            {
               "id": 4152,
               "rank": 3
            },
            {
               "id": 4122,
               "rank": 3
            },
            {
               "id": 4141,
               "rank": 1
            },
            {
               "id": 4111,
               "rank": 1
            },
            {
               "id": 4132,
               "rank": 1
            },
            {
               "id": 4232,
               "rank": 1
            },
            {
               "id": 4162,
               "rank": 1
            },
            {
               "id": 4131,
               "rank": 1
            }
         ],
         "id": 34787715,
         "name": "vi/j4/wuk/xin/noc",
         "current": false
      },
      {
         "masteries": [
            {
               "id": 4212,
               "rank": 2
            },
            {
               "id": 4353,
               "rank": 3
            },
            {
               "id": 4211,
               "rank": 2
            },
            {
               "id": 4311,
               "rank": 1
            },
            {
               "id": 4362,
               "rank": 1
            },
            {
               "id": 4322,
               "rank": 3
            },
            {
               "id": 4334,
               "rank": 1
            },
            {
               "id": 4332,
               "rank": 1
            },
            {
               "id": 4352,
               "rank": 1
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4314,
               "rank": 1
            },
            {
               "id": 4221,
               "rank": 1
            },
            {
               "id": 4331,
               "rank": 3
            },
            {
               "id": 4324,
               "rank": 1
            },
            {
               "id": 4313,
               "rank": 3
            },
            {
               "id": 4232,
               "rank": 1
            },
            {
               "id": 4342,
               "rank": 1
            },
            {
               "id": 4341,
               "rank": 1
            }
         ],
         "id": 34787716,
         "name": "Support",
         "current": false
      },
      {
         "masteries": [
            {
               "id": 4211,
               "rank": 2
            },
            {
               "id": 4214,
               "rank": 2
            },
            {
               "id": 4124,
               "rank": 1
            },
            {
               "id": 4114,
               "rank": 1
            },
            {
               "id": 4112,
               "rank": 4
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4113,
               "rank": 4
            },
            {
               "id": 4122,
               "rank": 3
            },
            {
               "id": 4152,
               "rank": 3
            },
            {
               "id": 4224,
               "rank": 1
            },
            {
               "id": 4132,
               "rank": 1
            },
            {
               "id": 4142,
               "rank": 3
            },
            {
               "id": 4232,
               "rank": 1
            },
            {
               "id": 4162,
               "rank": 1
            }
         ],
         "id": 34787717,
         "name": "AD Jungle",
         "current": false
      },
      {
         "masteries": [
            {
               "id": 4212,
               "rank": 2
            },
            {
               "id": 4211,
               "rank": 2
            },
            {
               "id": 4121,
               "rank": 1
            },
            {
               "id": 4134,
               "rank": 3
            },
            {
               "id": 4124,
               "rank": 1
            },
            {
               "id": 4114,
               "rank": 1
            },
            {
               "id": 4222,
               "rank": 3
            },
            {
               "id": 4112,
               "rank": 4
            },
            {
               "id": 4221,
               "rank": 1
            },
            {
               "id": 4122,
               "rank": 3
            },
            {
               "id": 4152,
               "rank": 3
            },
            {
               "id": 4141,
               "rank": 1
            },
            {
               "id": 4142,
               "rank": 1
            },
            {
               "id": 4132,
               "rank": 1
            },
            {
               "id": 4232,
               "rank": 1
            },
            {
               "id": 4162,
               "rank": 1
            },
            {
               "id": 4131,
               "rank": 1
            }
         ],
         "id": 34787718,
         "name": "ADC",
         "current": false
      },
   ],
   "summonerId": 23591778
}}

String[] array = new String[sizeX]; is not an array of arrays, it is an array of String, so array[i] = new String[sizeY]; is going to give you a type mismatch error. — azurefrog
– azurefrog, Commented May 5, 2014 at 14:33
@azurefrog You're right. I just typed up the code real quick to get my point across. Still half asleep. I'll fix it. — Nate
– Nate, Commented May 5, 2014 at 14:35
Why are the objects of different lengths in the JSON array? Could you show your exact use case? What's contained in the JSON array? — Joffrey
– Joffrey, Commented May 5, 2014 at 15:18
@Joffrey The length of the object is different because the JSON doesn't return parts it doesn't have an ID for. To go along with the, the way the points can be distributed into these ID's is variable. This is what is causing the issue. — Nate
– Nate, Commented May 5, 2014 at 15:27
@Nate I still don't get your use case. Can you elaborate a bit in your question? Maybe post part of your JSON, please. Do you have arrays in your JSON array, or just objects with properties? Why would these objects be of different types? If the problem is just that some properties are missing, then why not parse your JSON objects as objects with some uninitialized fields, instead of using the 2nd dimension to index properties? — Joffrey
– Joffrey, Commented May 5, 2014 at 15:33

Joffrey · Accepted Answer · 2014-05-05 16:16:57Z

UPDATE: since you updated your post with more info, here is my new answer.

You don't have a JSON array of JSON arrays, but an array of JSON objects. These objects, in turn, have one property that is a map (I believe), but it does not matter. You're trying to use a 2D-array instead of a 1D-array of objects.

Create a class to represent your objects:

public class MasteryPage {
    private long id;
    private String name;
    private boolean current;
    private Map<Long,Integer> masteries = new HashMap<>();

    public MasteryPage(long id, String name, boolean current) {
        this.id = id;
        this.name = name;
        this.current = current;
    }

    public void addMastery(long id, int rank) {
        masteries.put(id, rank);
    }

    // add getters/setters...      
}

Then use your class to create the array:

JSONArray jArray = json.getJSONArray("pages");
MasteryPage[] arr = new MasteryPage[jArray.length()];
for (int i = 0; i < jArray.length(); i++) {
    JSONObject jsonMasteryPage = jArray.getJSONObject(i);
    long id = jsonMasteryPage.getLong("id");
    String name = jsonMasteryPage.getString("name");
    boolean current = jsonMasteryPage.getBoolean("current");
    MasteryPage page = new MasteryPage(id, name, current);
    JSONArray jsonMasteries = jsonMasteryPage.getJSONArray("masteries");
    for (int j = 0; j < jsonMasteries.length(); j++) {
        JSONObject jsonMastery = jsonMasteries.getJSONObject(i);
        page.addMastery(jsonMastery.getLong("id"), jsonMastery.getInt("rank"));
    }
    arr.add(page);
}

You can then create each mastery page and parse the JSON to fill its fields.

Anubian Noob · Accepted Answer · 2014-05-05 14:39:20Z

0

Declare it like this:

String[][] arr = new String[][numRows];

And then add arrays to it by either of the following means:

arr[0] = new String[lengthOfJSONArray];
arr[0] = getStringArray();

answered May 5, 2014 at 14:39

Anubian Noob

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1 Comment

Joffrey Over a year ago

I think you meant new String[numRows][];

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