I am new to lambda expressions and I have this code to scan Eddystone beacons and I want to remove the lambda expression from it. I don't know exactly how they work. Can anyone help?

 beaconManager.getRegionViewModel(myRegion).getRangedBeacons().observe(this, beacons -> {
            noBeacons.setText(String.valueOf(beacons.size()));

            for (Beacon beacon : beacons) {
                if (uuids.contains(beacon))
                    continue;
                uuids.add(beacon);
                if (beacon.getServiceUuid() == 0xfeaa && beacon.getBeaconTypeCode() == 0x00) {
                    // This is a Eddystone-UID frame
                    Identifier namespaceId = beacon.getId1();
                    Identifier instanceId = beacon.getId2();
                    logthis("I see a beacon transmitting namespace id: "   namespaceId  
                            " and instance id: "   instanceId  
                            " approximately "   beacon.getDistance()   " meters away.");
                }
            }
        });

CodePudding user response：

The second parameter of the observe method is a functional interface, thats why you can put a lambda in it. Most likely it will be Consumer<T> from the java.util.function package because it takes just one argument beacons. If you want that lambda removed (i guess you mean replaced) you would need to define a class which implements this functional interface, like:

class Helper implements Consumer<Beacon[]> {
    @Override
    public void accept​(Beacon[] beacons) {
        // lambda body here
    }
}

and give an instance of the class to observe:

beaconManager.getRegionViewModel(myRegion).getRangedBeacons().observe(this, new Helper());

You could also do it in a more inline fashion with anonymous interface implementations, like so:

beaconManager.getRegionViewModel(myRegion).getRangedBeacons().observe(this, new Consumer<Beacon[]>() {
    public void accept(Beacon[] beacons) {
        // lambda body here
    }
});

But now you see there is no point in going this detour if not forced (read Java <8). Just learn a bit lambda syntax which is basically () -> {} and it does all the hassle for you.