Android WIFI How To Detect When Specific WIFI Connection is Available

You can use BroadcastReceiver to find out that wifi network has changed:

BroadcastReceiver broadcastReceiver = new WifiBroadcastReceiver();

IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION);
context.registerReceiver(broadcastReceiver, intentFilter);

The BroadcastReceiver may look like this.
And to check for specific MAC address see the checkConnectedToDesiredWifi() method bellow.

public class WifiBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (WifiManager.SUPPLICANT_STATE_CHANGED_ACTION .equals(action)) {
            SupplicantState state = intent.getParcelableExtra(WifiManager.EXTRA_NEW_STATE);
            if (SupplicantState.isValidState(state) 
                    && state == SupplicantState.COMPLETED) {

                boolean connected = checkConnectedToDesiredWifi();
            }
        }
    }

    /** Detect you are connected to a specific network. */
    private boolean checkConnectedToDesiredWifi() {
        boolean connected = false;

        String desiredMacAddress = "router mac address";

        WifiManager wifiManager = 
            (WifiManager) context.getSystemService(Context.WIFI_SERVICE);

        WifiInfo wifi = wifiManager.getConnectionInfo();
        if (wifi != null) {
            // get current router Mac address
            String bssid = wifi.getBSSID();
            connected = desiredMacAddress.equals(bssid);
        }

        return connected;
    }
}