android 再按一次后退键退出应用程序

private static Boolean isExit = false;

    private static Boolean hasTask = false;

    Timer tExit = new Timer();

    TimerTask task = new TimerTask() {

          

        @Override

        public void run() {

            isExit = false;

            hasTask = true;

        }

    };

      

    @Override

    public boolean onKeyDown(int keyCode, KeyEvent event) {

        System.out.println("TabHost_Index.java onKeyDown");

        if (keyCode == KeyEvent.KEYCODE_BACK) {

            if(isExit == false ) {

                isExit = true;

                Toast.makeText(this, "再按一次后退键退出应用程序", Toast.LENGTH_SHORT).show();

                if(!hasTask) {

                    tExit.schedule(task, 2000);

                }

            } else {

                finish();

                System.exit(0);

            }

        }

        return false;

    }