How to add session in android application? -

i'm making android application in there different activities connected home (mainactivty) activity , vice-verse. want close application whenever press key home activity. takes me previous activity came from. how can this. please me in this, i'm new android. thanks.............

here code:

  btn_daily.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view view) {              intent = new intent(getapplicationcontext(), activitya.class);             startactivity(i);         }     });      btn_health.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view view) {              intent = new intent(getapplicationcontext(), activityb.class);             startactivity(i);         }     });      btn_diet.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view view) {              intent = new intent(getapplicationcontext(), activityc.class);             startactivity(i);         }     });      btn_exercise.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view view) {              intent = new intent(getapplicationcontext(), activityd.class);             startactivity(i);         }     });      btn_yoga.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view view) {              intent = new intent(getapplicationcontext(), activitye.class);             startactivity(i);         }     });      btn_help.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view view) {              intent = new intent(getapplicationcontext(), activityf.class);             startactivity(i);         }     }); }  @override public boolean oncreateoptionsmenu(menu menu) {      // inflate menu; adds items action bar if present.     getmenuinflater().inflate(r.menu.main, menu);     return true; }   public boolean onkeydown(int keycode, keyevent event) {     if (keycode == keyevent.keycode_back) {         dialogonbackpress();          return true;     }     return super.onkeydown(keycode, event); }  protected void dialogonbackpress() {      new alertdialog.builder(this)             .settitle("exit alert !!")            .setmessage("are sure want exit?")            .setcancelable(false)            .setpositivebutton("yes", new dialoginterface.onclicklistener() {                public void onclick(dialoginterface dialog, int id) {                     finish();                }            })            .setnegativebutton("no", null)            .show();  } 

it seems activities other mainactivity, has mechanism navigate other activities. while navigating other activity, don't forget use finish() destroy current activity.

and if application has other mechanism there home button takes home screen navigation activity, @ time open mainactivity flag_activity_clear_top flag.

hence doing so, not have stack of activity , button mainactivity close app.

edit : scenario have mentioned in comment, have use following code on home button click.

 btn_home.setonclicklistener(new view.onclicklistener() {      @override     public void onclick(view view) {          intent = new intent(currentactivity.this, mainactivity.class);         i.setflags(intent.flag_activity_clear_top);         startactivity(i);         finish();     } });