java - AuthError On YouTube Search List Execute -

i exploring youtube api , creating java application can search authorized users token. authorization follows.

private static credential authorize(string storedirectory) throws exception {     // load client secrets      yt.data_store_dir = new java.io.file(".",".store/"+storedirectory);     yt.datastorefactory = new filedatastorefactory(yt.data_store_dir);      googleclientsecrets clientsecrets = googleclientsecrets.load(yt.json_factory,         new inputstreamreader(new bytearrayinputstream(yt.client_secret_json.getbytes(standardcharsets.utf_8))));     if (clientsecrets.getdetails().getclientid().startswith("enter")         || clientsecrets.getdetails().getclientsecret().startswith("enter ")) {       system.out.println(           "enter client id , secret https://code.google.com/apis/console/?api=plus "           + "into client string.");       system.exit(1);     }      string[] permissoins = { plusscopes.plus_login, plusscopes.plus_me, plusscopes.userinfo_email, plusscopes.userinfo_profile, "https://www.googleapis.com/auth/youtube" };     // set authorization code flow     googleauthorizationcodeflow flow = new googleauthorizationcodeflow.builder(         yt.httptransport, yt.json_factory, clientsecrets,         new arraylist(arrays.aslist(permissoins))).setdatastorefactory(         yt.datastorefactory).build();     // authorize     return new authorizationcodeinstalledapp(flow, new localserverreceiver()).authorize("user"); } 

i trying search single keyword bellow

credential credential = authorize("username"); youtube.search.list search = youtube.search().list("id,snippet"); // have set oauthtoken here.  search.setoauthtoken(credential.getaccesstoken()); search.setmaxresults(50l); search.setq("search keyword"); search.settype("video"); search.setfields("items(id/kind,id/videoid,snippet/title,snippet/thumbnails/default/url)"); // exception below line. searchlistresponse searchresponse = search.execute(); list<searchresult> searchresultlist = searchresponse.getitems(); 

i getting exception details below.

ex = (com.google.api.client.googleapis.json.googlejsonresponseexception) com.google.api.client.googleapis.json.googlejsonresponseexception: 401 unauthorized {   "code" : 401,   "errors" : [ {     "domain" : "global",     "location" : "authorization",     "locationtype" : "header",     "message" : "invalid credentials",     "reason" : "autherror"   } ],   "message" : "invalid credentials" } 

i wondering missing set api key or else wrong.

do need use

search.setkey("youtube_developer_key");

i confused use youtube_developer_key ?