multi select spinner clearAll button android -

i'm creating multi select spinner , got problem clear button http://postimg.org/image/eoyq5jpib/ "select all" work pretty when clicked on "clear all" nothing happens. why i'm getting problem "clear all"?

protected charsequence[] _options = { "one", "two", "three", "four", "five" }; protected boolean[] _selections =  new boolean[ _options.length ]; protected button _optionsbutton;   public class buttonclickhandler implements view.onclicklistener {     public void onclick( view view ) {         showdialog( 0 );     } }  @override protected dialog oncreatedialog( int id ) {     return             new alertdialog.builder( )                     .settitle( "students" )                     .setmultichoiceitems(_options, _selections, new dialogselectionclickhandler())                     .setpositivebutton("ok", new dialogbuttonclickhandler())                     .setneutralbutton("select all",                             new dialoginterface.onclicklistener() {                                 @override                                 public void onclick(dialoginterface dialog, int which) {                                     selectallstudents();                                 }                             })                     .setnegativebutton("clear all",                             new dialoginterface.onclicklistener() {                                 @override                                 public void onclick(dialoginterface dialog, int which) {                                     clearallstudents();                                 }                             })                     .create();  }   public class dialogselectionclickhandler implements dialoginterface.onmultichoiceclicklistener {     public void onclick( dialoginterface dialog, int clicked, boolean selected )     {         log.i("me", _options[clicked] + " selected: " + selected);     } }   public class dialogbuttonclickhandler implements dialoginterface.onclicklistener {     public void onclick( dialoginterface dialog, int clicked )     {         checkallstudents();         switch( clicked )         {             case dialoginterface.button_positive:                 printselectedstudents();                 break;             case dialoginterface.button_neutral:                 printselectedstudents();                 break;             case dialoginterface.button_negative:                 printselectedstudents();                 break;         }     } }  protected void clearallstudents(){     (int = 0; i<_options.length; i++) {         _selections[i] = false;     } }  protected  void selectallstudents(){     (int = 0; i<_options.length; i++) {         _selections[i] = true;     } } protected void printselectedstudents(){     for( int = 0; < _options.length; i++ ){         log.i( "me", _options[ ] + " selected: " + _selections[i] );