Why doesn't the if, else if, else logic work in AsyncTask in the doInBackground method?

Question

Android

There is no "RUB" Currency in Json. Decided to register manually. But when selecting " RUB " in the spinner and passing this value to doInBackground , the logic does not work, a NullPointerException is thrown.

@Override
    protected String doInBackground(String... params) {
        Call<JsonObject> request = callObject.call();
        JsonObject Value2;
        JsonObject Value1;


        try {
            Response<JsonObject> response = request.execute(); 
            JsonObject reader = response.body();
            JsonObject Valute = reader.getAsJsonObject("Valute");
            double a=1.0;
            if (params[0]=="RUB") {
                Value2 = Valute.getAsJsonObject(params[1]);
                out = String.valueOf(Precision.round(a/Value2.get("Value").getAsDouble(),3));
                return out;
            }
            else if (params[1]=="RUB"){
                Value1 = Valute.getAsJsonObject(params[0]);
                out = String.valueOf(Precision.round(Value1.get("Value").getAsDouble()/a,3));
                return out;
            }
            else if (params[0]=="RUB" & params[1]=="RUB") { out = String.valueOf(1.0);
                 return out;
             }
            else {
                Value1 = Valute.getAsJsonObject(params[0]);
                Value2 = Valute.getAsJsonObject(params[1]);
                out = String.valueOf(Precision.round(Value1.get("Value") //Использовал библиотеку
                        .getAsDouble()/Value2.get("Value").getAsDouble(),3));// APACH для округления чисел
                return out;
            }


        } catch (IOException e) {
            e.printStackTrace();
        }
        return out;
    }

Answer 1

1. As far as I remember, in java, you should not compare strings like this
params[0]=="RUB"
for this there is equals,
even if it is an attempt to compare by reference
2. I guess you are not writing in a notepad,
put a breakpoint on the first line of the method,
yes take a look at what comes into the variables