I made it that way:

if I have:

var jsonArg1 = new Object();
    jsonArg1.name = 'calc this';
    jsonArg1.value = 3.1415;
var jsonArg2 = new Object();
    jsonArg2.name = 'calc this again';
    jsonArg2.value = 2.73;

var pluginArrayArg = new Array();
    pluginArrayArg.push(jsonArg1);
    pluginArrayArg.push(jsonArg2);

to convert pluginArrayArg (which is pure javascript array) into JSON array:

var jsonArray = JSON.parse(JSON.stringify(pluginArrayArg))

Input String

[
   {
      "userName": "sandeep",
      "age": 30
   }, 
   {
      "userName": "vivan",
      "age": 5
   }
]

Simple Way to Convert String to JSON

public class Test
{

    public static void main(String[] args) throws JSONException
    {
        String data = "[{\"userName\": \"sandeep\",\"age\":30},{\"userName\": \"vivan\",\"age\":5}]  ";
        JSONArray jsonArr = new JSONArray(data);

        for (int i = 0; i < jsonArr.length(); i++)
        {
            JSONObject jsonObj = jsonArr.getJSONObject(i);

            System.out.println(jsonObj);
        }

    }
}

Output

{"userName":"sandeep","age":30}
{"userName":"vivan","age":5}

Simplest and correct code is:

public static String[] toStringArray(JSONArray array) {
    if(array==null)
        return new String[0];
    
    String[] arr=new String[array.length()];
    for(int i=0; i<arr.length; i++) {
        arr[i]=array.optString(i);
    }
    return arr;
}

Using List<String> is not a good idea, as you know the length of the array. Observe that it uses arr.length in for condition to avoid calling a method, i.e. array.length(), on each loop.

As simple as that.

var str = '{"id":1,"name":"Test1"},{"id":2,"name":"Test2"}';
 dataObj = JSON.parse(str);