android app 点击2次退出应用程序代码

private long exitTime = 0;

/**
* 重写返回按钮
*/
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
int codekey = event.getKeyCode();

if (codekey == KeyEvent.KEYCODE_BACK
&& event.getAction() == KeyEvent.ACTION_DOWN) {
System.out.println(exitTime);
if ((System.currentTimeMillis() - exitTime) > 2000) {
Toast.makeText(getApplicationContext(),
getString(R.string.tip_again), Toast.LENGTH_SHORT)
.show();
exitTime = System.currentTimeMillis();
} else {

System.out.println("进入else,退出程序");
System.exit(0);

}
return true;
}
return super.dispatchKeyEvent(event);
}