android两次按回来键退出程序实现

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;        }    };public boolean onKeyDown(int keyCode, KeyEvent event) {                // TODO Auto-generated method stub                if(keyCode == KeyEvent.KEYCODE_BACK){//                        System.out.println("user back down");                        if(isExit == false ) {                                isExit = true;                                Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();                                if(!hasTask) {                                        tExit.schedule(task, 2000);                                }} else {                                                                                }                                finish();                                System.exit(0);                        }                }                                        return false;        }

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public boolean onKeyDown(int keyCode, KeyEvent event) {		if(keyCode == KeyEvent.KEYCODE_BACK){			if(isExit == false){				isExit = true;				Toast.makeText(this, R.string.tip_back_exit, Toast.LENGTH_SHORT).show();				if(!hasTask){					tExit.schedule(task, 2000);				}			}else{				finish();				System.exit(0);			}		}		return false;	}