android - AsyncTask.execute() returns null -

i using below code version json

webservice.java

public void getsingleresponse(final string url) {         class task extends asynctask<string, string, string> {             @override             protected string doinbackground(string... params) {                 // todo auto-generated method stub                 string resp;                 resp = "";                 httpclient httpclient = new defaulthttpclient();                 try {                     log.d("url", "" + params[0]);                     httpresponse response = httpclient.execute(new httpget(                             params[0]));                     httpentity entity = response.getentity();                     log.d("entity ", "" + entity);                     string responsestring = entityutils.tostring(entity,                             "utf-8");                     resp = responsestring;                     globalvar.version = resp;                     log.v("global version", "" + globalvar.version);                 } catch (exception e) {                     // todo: handle exception                     log.v("http:::::", "error" + e.getcause());                 }                 return globalvar.version;             }         }         new task().execute(url);     } 

mainactivity.java

public static string getmarketversion() throws jsonexception {         string version = "";         try {             webservice ws = new webservice();             string serverurl = server_url + "/getversion";             log.i(tag, "server url" + serverurl);              ws.getsingleresponse(serverurl);             string response = globalvar.version;             log.v("response :: ", "version ::" + response);              jsonarray jarry = new jsonarray(response);             jsonobject jobj = jarry.getjsonobject(0);             version = jobj.getstring("version");              log.v("parsing ", "version :: " + version);             return version;          } catch (exception e) {             e.printstacktrace();         }         return version;     } 

when run application got version blank see log below

07-24 12:27:42.309: v/response ::(4268): version :: 07-24 12:27:43.389: v/global version(4268): [{"version":"1.1.3"}] 

but when debug application able get response

07-24 12:06:01.699: v/global version(3122): [{"version":"1.1.3"}] 07-24 12:06:07.349: v/response ::(3122): version ::[{"version":"1.1.3"}] 07-24 12:08:12.019: v/parsing(3122): version :: 1.1.3 

i don't know whats going on in advance

first try understand, how asynctask works? doinbackground works in different thread ui thread, , after execute asynctask have wait until complete, means need override onpostexecute method of asynctask , there version, , btw should not share things using static variable in android , android provide various methods that