android - second activity still remains in session after logout -

i developing apps in android. in have login , logout activity session management using sharedpreferences. apps logout , store data in sharedpreferences maintain session done. when logout apps(second activity) , rendered first activity(login activity ) happen when clicked button on emulator after logout still again rendered second activity , version 2.3.3 etc encountered exception

java.lang.runtimeexception: unable destroy activity {com.oj.bs/com.oj.bs.loginactivity}: java.lang.nullpointerexception 

can fix problem. please refer following code

following login activity code

sessionmngr = new sessionmanager(getapplicationcontext());                      jsonobject json_user = jsonobj.getjsonobject("user");                     sessionmngr.createloginsession(id,json_user.getstring(key_uname),                              json_user.getstring(key_uemail));                      .                      . 

following session management

public class sessionmanager {  sharedpreferences pref; editor editor; context contxt; //shared pref mode int private_mode = 0;  // sharedpref file name private static final string pref_name = "bookingscapepref";  // shared preferences keys private static final string is_login = "isloggedin"; public static final string key_name = "name"; public static final string key_id = "id"; public static final string key_email = "email";  public sessionmanager(context context) {     super();     this.contxt = context;     pref = context.getsharedpreferences(pref_name, private_mode);     editor = pref.edit();     editor.commit(); } /**  * create login session  * */ public void createloginsession(int id,string name, string email) {      editor.putboolean(is_login,true);     editor.putstring(key_name, name);     editor.putstring(key_email, email);     editor.putint(key_id, id);     editor.commit(); } /**  * stored session data  * */ public hashmap<string, string> getuserdetails() {     hashmap<string, string> userdetails = new hashmap<string, string>();     userdetails.put(key_name, pref.getstring(key_name, null));     userdetails.put(key_email, pref.getstring(key_email, null));     return userdetails; } /**  * check login method check user login status  * */ public void checklogin() {      if (!this.isloggedin()) {         intent = new intent(contxt, loginactivity.class);         //closing activity         i.addflags(intent.flag_activity_clear_top);         //add new flag start new activity         i.setflags(intent.flag_activity_new_task);          contxt.startactivity(i);     } }  public void logoutuser() {     //clearing data sharedpreferences     editor.clear();     editor.commit();     intent intnt = new intent(contxt, loginactivity.class);     // closing activities     intnt.addflags(intent.flag_activity_clear_top);      // add new flag start new activity     intnt.setflags(intent.flag_activity_new_task);      // staring login activity     contxt.startactivity(intnt); }  /**  * quick check login  * **/ // login state public boolean isloggedin(){     return pref.getboolean(is_login, false); } 

}

this second activity here i'm checking session

public class projectfragactivity extends sherlockfragmentactivity {  sessionmanager sessionmngr ; @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);      sessionmngr = new sessionmanager(getapplicationcontext());      toast.maketext(getapplicationcontext(), "user login status: " + sessionmngr .isloggedin(),              toast.length_long).show();     sessionmngr.checklogin();             .             . 

i don't know how session , working, bt, try use finish() function while doing logout action, action not there while button presses