Loading JSON from String into JSONArray on Android

A few problems I can see:

1. You use jsonObj on the first line, which is a JSONObject. Then in the for loop, you use a different object called json. I'm going to assume that these two are the same object. Otherwise, there is information missing from your example.
2. JSONObject does not have a method get that takes an integer. There is one that takes a string, so I will assume you meant that one.
3. JSONObject.get returns the data corresponding to the key you give it. It returns an Object.

The error you are getting is because you are trying to cast an JSONObject to a Kabelskap.

What I would do is create a helper method like below. Alternatively, you could create a special constructor on the Kabelstap object.

public Kabelskap getKabelskapFromJSON(JSONObject jsonObj)
{
    Kabelskap k = new Kabelskap();

    String driftsmerking = jsonObj.getString("driftsmerking");
    k.setDriftsmerking(driftsmerking);

    String addresse = jsonObj.getString("addresse");
    k.setAddresse(addresse);

    String objektnummer = jsonObj.getString("objektnummer");
    k.setObjektNummer(objektnummer);

    double spenning = jsonObj.getDouble("spenning");
    k.setSpenning(spenning);

    // ... and so on for each property.

    return k;
}

which can then be used like so:

try {
    JSONArray jsonArray = new JSONArray(yourJSONString);
    for(int i = 0; i < jsonArray.length(); i++)
    {
        JSONObject jsonObj = jsonArray.getJSONObject(i);
        Kabelskap k = getKabelskapFromJSON(jsonObj);
        // do something with k. eg
        System.out.println("Kabelskap@"+i+": "+k);
    }
} catch (JSONException e) {
    e.printStackTrace();
}

Documentation for JSONObject is here and JSONArray is here.