将Object ArrayList转换为Double List的最佳方法是什么

Question

I've started to learn Java/Android and I am trying to gather RSSI values of bluetooth devices. I have 2 fragments on the same activity and every device I discover I show on a listview and keep collecting the data in a ArrayList which holds my object class. later when I want to visualize the data for a device, I need to convert this object array list to ArrayList to get only RSSI values and show on the second fragment. My Problem is this conversion made my screens very slow. Any suggestions? Thank you

This is the function , I think it makes it slow;

public static ArrayList<Double> extractDeviceRSSIOnly(ObjDevice device,
        ArrayList<ObjDevice> list)
{
    ArrayList<Double> selectedList=new ArrayList<Double>();
    if(device!=null&& list!=null) {
        if (list.size() > 0) {
            for(int i=0;i<list.size();i++)
            {
                if(list.get(i).get_macAddress().equals(device.get_macAddress())) {
                    selectedList.add(list.get(i).get_signalStrength());
                }
            }
        }
        return selectedList;
    }
}

Answer 1

Your code looks good. You can make it a tiny bit more efficient by avoiding calling get(i) twice. The enhanced for will help you with that, and will give you a cleaner code.

As suggested by @Makoto, you can avoid the list.size() > 0 test too. An empty list will simply not iterate.

if (device != null && list != null) {
    for (ObjDevice objDevice : list) {
        if (objDevice.get_macAddress().equals(device.get_macAddress())) {
            selectedList.add(objDevice.get_signalStrength());
        }
    }
}