Q:

Add new objects in arraylist to the other arraylist while the second one do not have these new objects

If I have two ArrayList one for currentScanWifiList<Router>
this contains the current wifi scan Routers data 
and the the second have the same type allUniqueRoutersList<Router>
used to add the new routers existing in currentScanWifiList and do not exist in allUniqueRoutersList
the comparing between the routers through equaling its bssid 

public class Router {
    private String bssid;//identifier
    private String ssid;
    private double x;
    private double y;
    private double meanRss;
setter and getter....
}
    for (int x = 0; x < currentScanList.size(); x++) {
        Router currentTempRouter = currentScanList.get(x);
        for (int y = 0; y < allUniqueRoutersList.size(); y++) {
            Router allTempRouter = currentScanList.get(y);
            if (!currentTempRouter.getBssid().equals(allTempRouter.getBssid())) {
                allUniqueRoutersList.add(currentScanList.get(x));
                break;
            } 
        }
    }

I tried this code but it is not working, it add all objects to allUniqueRoutersList
not the new ones only 
what should I do to compare between the two arraylist elements using bssid

A:

This is because you add the router immediately, e.g. you don't really loop:
for (int x = 0; x < currentScanList.size(); x++) {
            Router currentTempRouter = currentScanList.get(x);
            boolean found = false;
            for (int y = 0; y < allUniqueRoutersList.size(); y++) {
                Router allTempRouter = allUniqueRoutersList.get(y);
                if (currentTempRouter.getBssid().equals(allTempRouter.getBssid())) {
                    found = true;
                    break;
                }
            }
            if(!found){
                allUniqueRoutersList.add(currentTempRouter);
            }
        }

