Android实现连按2次返回键退出

private long d = 0;

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if(keyCode == KeyEvent.KEYCODE_BACK){
long date = new Date().getTime();
exit(date);
return false;
}
return super.onKeyDown(keyCode, event);
}

public void exit(long date){
if(date - d < 2000){
finish();
}else{
d = date;
Toast.makeText(Indexactivity.this, R.string.exit22, Toast.LENGTH_SHORT).show();
}
}