android - java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT (Retrofit 2) -

i such error: java.lang.illegalstateexception: expected begin_array begin_object, when receive data server. can cause such error? , how fix it?

json receive server:

{   "group": [     {       "name": "group1",       "description": "test group 1"     },     {       "name": "group2",       "description": "group name updated"     }   ] } 

here api interface:

@get("groups")     observable <list<group>> getallgroups(@header("authorization") string auth,                                    @header("content-type") string contenttype,                                    @header("accept") string accept                                   ); 

method receive data:

private void getallgroups() {     string credentials = "admin" + ":" + "admin";     final string basic =             "basic " + base64.encodetostring(credentials.getbytes(), base64.no_wrap);     string contenttype = "application/json";     string accept = "application/json";     subscription subscription = app.service.getallgroups(basic, contenttype, accept)             .subscribeon(schedulers.io())             .observeon(androidschedulers.mainthread())             .subscribe(groups -> {                 grouplist.addall(groups);             }, throwable -> {                 log.e("all group error", string.valueof(throwable));             });      addsubscription(subscription); } 

class group:

public class group {      private string name;     private string description;      public group(string name, string description) {         this.name = name;         this.description = description;     }  } 

i added class groups:

public class groups {      @serializedname("group")     list<group> group; } 

and changed code in api interface to:

 @get("groups")     observable <groups> getallgroups(@header("authorization") string auth,                                    @header("content-type") string contenttype,                                    @header("accept") string accept                                   ); 

and after app starts work without errors.