//1.声明变量

	// 退出时间

	private long currentBackPressedTime = 0;

	// 退出间隔

	private static final int BACK_PRESSED_INTERVAL = 2000;

	//   2、重写onBackPressed()方法

	@Override

	public void onBackPressed() {

		// 判断时间间隔

		if (System.currentTimeMillis() - currentBackPressedTime > BACK_PRESSED_INTERVAL) {

			currentBackPressedTime = System.currentTimeMillis();

			Toast.makeText(this, "再按一次返回键退出程序", Toast.LENGTH_SHORT).show();

		} else {

			// 销毁

			finish();

		}

	}