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;
	}

public boolean onKeyDown(int keyCode, KeyEvent event) {
		if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
			if ((System.currentTimeMillis() - exitTime) > 2000) {
				Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
				exitTime = System.currentTimeMillis();
			} else {
				finish();
			}
		}
		return false;
	}