android - Webpage not showing last webpages when i click on back button -

i want know operation when user hits button while using web view in his/her android application. code using activity. please suggest me should change in code or should add different code snippet in activity.

 public class webview_activity extends activity     {             progressdialog pbhg;         webview web;         protected void oncreate(bundle savedinstancestate)          {             super.oncreate(savedinstancestate);             setcontentview(r.layout.webview11);              getactionbar().settitle("notifications");             getactionbar().seticon(r.drawable.phnxlogg);                 web=(webview)findviewbyid(r.id.webview1);             web.getsettings().setjavascriptenabled(true);             web.setlongclickable(false);             web.setwebviewclient(new webviewclient());              telephonymanager tmw = (telephonymanager) getsystemservice(context.telephony_service);             string imeie = tmw.getdeviceid();               //string value=getintent().getextras().getstring("orderid");             //toast.maketext(getapplicationcontext(), value, toast.length_long).show();                  sharedpreferences pref = getsharedpreferences(prefs_name,mode_private);                    string username = pref.getstring(pref_username, "null");                 string password = pref.getstring(pref_password, "null");                    web.loadurl("url");         /*******back key operation*********/          public boolean onkeydown(int keycode, keyevent event) {             if ((keycode == keyevent.keycode_back) && this.web.cangoback()) {                   // web.loadurl("http://www.mobitalktime.com/offers.php?id="+vh1+"&salt="+vh2+"&deviceid="+vh3);                  this.web.goback();                 return true;             }              return super.onkeydown(keycode, event);         }          /*******back key operation*********/       } 

when try hit button shows main page, want let user show whole web pages he/she has gone through yet when clicks back.

check this:

 @override          public boolean onkeydown(int keycode, keyevent event) {             // check if key event button , if there's history             if ((keycode == keyevent.keycode_back) && mywebview.cangoback()) {                 mywebview.goback();                 return true;             }             // if wasn't key or there's no web page history, bubble default             // system behavior (probably exit activity)             return super.onkeydown(keycode, event);         }