Json rpc claculator - json

Question

My main activity: I have created threads and handler and tried calling it to establish a connection to a particular server:
public void mResult (){
Double secondNum = Double.parseDouble(screenView.getText().toString());
Double result = 0.0;
this.result=result;
// thread call
android.os.Handler aHandler = new android.os.Handler();
DoCalc myCalc = new DoCalc(aHandler, firstNum, secondNum, Operation);
myCalc.start();
screenView.setText(String.valueOf(result));
}
my main thread
class DoCalc extends Thread {
private android.os.Handler handler;
private double left,right;
private String oper;
public DoCalc(android.os.Handler myHandle, double left, double right, String oper){
this.handler = myHandle;
this.left = left;
this.right = right;
this.oper = oper;
}
public DoCalc(Handler aHandler, Double firstNum, Double secondNum, String operation){
this.handler = aHandler;
this.left = firstNum;
this.right = secondNum;
this.oper = operation;
}
public void run(){
Double result = 0.0;
String url = "http://129.219.151.99:8080/JsonRPC/calc";
try{
HttpJsonRpcClientTransport transport =
new HttpJsonRpcClientTransport(new URL(url));
transport.call(url);
LoggingPermission JsonRpcInvoker;
org.json.rpc.client.JsonRpcInvoker invoker = new JsonRpcInvoker();
Calculator calc = invoker.get(transport, "calc", Calculator.class);
if(oper.equals("+")){
result = calc.add(left,right);
}
if(oper.equals("-")){
result = calc.subtract(left, right);
}
if(oper.equals("*")){
result = calc.multiply(left, right);
}
if(oper.equals("/")){
result = calc.divide(left, right);
}
//FinalResult set = new FinalResult(result);
handler.post(new FinalResult(result));
// set.start();
}catch (Exception ex){
android.util.Log.w("calc","exception in call: "+ex.getMessage());
}
}
class FinalResult extends Thread implements Runnable {
double result;
EditText screenView;
public FinalResult(double result){
this.result = result;
}
public void run(){
android.util.Log.w("calc","result is: "+result);
System.out.println("result is"+result);
screenView.setText(String.valueOf(result));
}
}
}
}
I think my json rpc is not working am just getting 0.0 when ever I do any calculation