CODEWITHSUNDEEP
java
Alvaro
Alvaro

Reputation: 41605

Create multi array in Java

This might be a very basic question but I'm not used to work with Java and I would like to create an array / list like this:

6546:{
    "Ram":{
         24M,
         4M,
         64M,
         ...
    },

    "Cpu":{
         2%,
         4%,
         6%,
         ...
    },
    ...
}

I've been trying it with LinkedList and so on but end up creating lists of lists and it starts looking very ugly.

This is a very common array in JSON, PHP or even Javascript, what would be the best way to create it by using Java?

Upvotes: 0

Views: 87

Answers (5)

ProgrammerDan
ProgrammerDan

Reputation: 901

This looks more like a key/value indexed structure.

One way (of many) to do something equivalent in Java:

Map<Integer, Map<String, String[]>> myData = new Hashtable<Integer, Map<String, String[]>>();
Map<String, String[]> entries = new Hashtable<String, String[]>();

entries.put("Ram", new String[] {"24M", "4M"}); // etc.
entries.put("Cpu", new String[] {"2%", "4%"}); // etc.

myData.put(6546, entries);

This would create an equivalent data structure, and you could index into it in a familiar fashion:

myData.get(6546).get("Ram")[0];

Although that would be VERY bad form, as you should always check for nulls before using the results of .get(x), such as:

Map<String, String[]> gotEntry = myData.get(6546);
if (gotEntry != null) {
    String[] dataPoints = gotEntry.get("Ram");

    if (dataPoints != null && dataPoints.length > 0) {
        String data = dataPoints[0];
     }
}

And so on. Hope this helps!

One other more interesting option is to use something like described here where you can define your data as a JSON string, and convert it into Object types later using un/marshalling.

Upvotes: 0

Muhammad Kashif Nazar
Muhammad Kashif Nazar

Reputation: 23945

HashMap<Integer, HashMap<String, List<Object>>> looks good.

Upvotes: 0

RMachnik
RMachnik

Reputation: 3694

It might be done in that way.

int[][] twoDimTable = new int[size][size];
String[][] twoDimTable = new String[size][size];

or
List<List<Integer> list = new ArrayList<>(); //or
List<List<String> list = new ArrayList<>();

Upvotes: 0

Subhrajyoti Majumder
Subhrajyoti Majumder

Reputation: 41240

Array of array you can define like - String[][].

Upvotes: 0

djechlin
djechlin

Reputation: 60848

You want a List<List<Integer>> or an int[][].

List<List<Integer>> list = new ArrayList<>();
list.add(new ArrayList<>());
list.get(0).add(24);

But perhaps you just want to use something like Gson and store this as JSON.

Or create a class like:

class Data {
    private final List<Integer> ram = new ArrayList<>();
    private final List<Integer> cpu = new ArrayList<>();
}

Or if you want to avoid creating classes? (Which you shouldn't) 

Map<String, List<Integer>> map = new HashMap<>();
map.put("cpu", new ArrayList<>());
map.put("ram", new ArrayList<>());

Upvotes: 1

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