Volley: Kotlin Class call from JavaCode

Question

I'd like to make simple Volley POST Requests due Java and Kotlin. I'm using both languages in my App so I tried do to my best to use both languages. I came over this tutorial with the following VolleyClass in Kotlin:

class WolfRequest(val url: String, val result: (JSONObject) -> Unit, val error: (String) -> Unit) {

fun POST(vararg params: Pair<String, Any>) {
    // HashMap to pass arguments to Volley
    val hashMap = HashMap<String, String>()
    params.forEach {
        // Convert all Any type to String and add to HashMap
        hashMap[it.first] = it.second.toString()
    }
    // Make the Http Request
    makeRequest(Request.Method.POST, hashMap)
}

private fun makeRequest(method: Int, params: HashMap<String, String>) {
    // Creating a StringRequest
    val req = object : StringRequest(method, url, { res ->

        // Creating JSON object from the response string
        // and passing it to result: (JSONObject) -> Unit function
        result(JSONObject(res.toString().trim()))
    }, { volleyError ->

        // Getting error message and passing it
        // to val error: (String) -> Unit function
        error(volleyError.message!!)
    }) {
        // Overriding getParams() to pass our parameters
        override fun getParams(): MutableMap<String, String> {
            return params
        }
    }

    // Adding request to the queue
    volley.add(req)
}

// For using Volley RequestQueue as a singleton
// call WolfRequest.init(applicationContext) in
// app's Application class
companion object {
    var context: Context? = null
    val volley: RequestQueue by lazy {
        Volley.newRequestQueue(context
                ?: throw NullPointerException(" Initialize WolfRequest in application class"))
    }

    fun init(context: Context) {
        this.context = context
    }
}

}

I'm trying to access this Code from a Java.Class to make a POST Reuqest:

    WolfRequest.Companion.init(getApplicationContext());
    HashMap <String, String> params = new HashMap <> ();
    params.put("id", "123");

    new WolfRequest(config.PING_EVENTS,*new WolfRequest()*
    {

        public void response(JSONObject response) {
            Log.e("Ping","PING");
        }

        public void error(String error) {
            Log.e("Ping",error);
        }
    }).POST(params);

It gives me an error here (new WolfRequest()) saying: Cannot inherit from final "...wolfrequest.kt"

I really don't get the error, what's the problem here?

Thank you

k5_ k5_ · Accepted Answer · 2019-07-11T20:46:15

Classes in kotlin are final by default. To create a none final class you need to declare it as open. So open class WolfRequest

With new WolfRequest() {} in java you create an anonymous class that extends WolfRequest, so you get that error inheriting from an final class.

To actually call the constructor for WolfRequest you need to pass the three arguments. Something like:

new WolfRequest("", (s) -> Unit.INSTANCE, (s) -> Unit.INSTANCE){
....
}

Volley: Kotlin Class call from JavaCode

1 Answers