Android双击返回键退出Activity

private long exitTime = 0;

	@Override
	public void onBackPressed() {
		// TODO Auto-generated method stub
		if ((System.currentTimeMillis() - exitTime) > 2000) {
			Toast.makeText(this, "再次按返回键退出", Toast.LENGTH_SHORT).show();
			exitTime = System.currentTimeMillis();
		} else {
			super.onBackPressed();
		}
	}