Android 再按一次退出应用程序

public boolean onKeyDown(int keyCode, KeyEvent event) {
		if (keyCode == KeyEvent.KEYCODE_BACK) {
			exitcount++;
			if (exitcount >= 1 && exitcount < 2) {
				exitsec = Utils.getNowSec();
				Utils.show(this, "再按一下退出程序！");
			} else {
				long exitnow = Utils.getNowSec();
				// Log.d("QX-sec",
				// String.valueOf(Math.abs(exitsec - exitnow)));
				if (Math.abs(exitsec - exitnow) > 3) { <span style="white-space:pre">	</span>//两次按back键时的时间间隔大于3的话
					exitcount = 0;
					Utils.show(this, "再按一下退出程序！");
				} else {<span style="white-space:pre">				</span><span style="font-family: Arial, Helvetica, sans-serif;">//两次按back键时的时间间隔小于3的话</span><span style="white-space:pre">
</span>					exitcount = 2;
				}
			}
			if (exitcount >= 2) {//如果按键次数大于或等于2时，退出程序
				exitcount = 0;
				finish();
				System.exit(0);
			}
			return true;
		} else {
			return super.onKeyDown(keyCode, event);
		}
	}