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Java: Mysterious Java uncaught exception handler [with code]
package staticexception;

import java.net.InterfaceAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
import javax.swing.UIManager;

public class StaticException {
    // Don't need this fully implemented.
    public static class IPAddress {

        public static IPAddress getBroadcast(IPAddress mask, IPAddress myip) {
            return new IPAddress();
        }

        public IPAddress() {}

        public IPAddress(int maskval) {}

        public IPAddress(byte[] addr) {}

        public IPAddress mask(IPAddress netmask) {
            return this;
        }

        public int prefixLength() {
            return 0;
        }

    }

    public static class Network {
        public IPAddress broadcast, netmask, ip;
        boolean remember;

        public Network(IPAddress br, IPAddress nm, IPAddress ip) {
            broadcast = br;
            netmask = nm;
            this.ip = ip;
        }

        boolean match(IPAddress ip) {
            IPAddress a = ip.mask(netmask);
            IPAddress b = this.ip.mask(netmask);
            return (a.equals(b));
        }

        @Override
        public String toString() {
            return ip.toString() + "/" + netmask.prefixLength();
        }
    }

    static List<Network> my_networks;

    static void enumerateNetworks() {
        my_networks = new ArrayList<Network>();

        Enumeration<NetworkInterface> nets = null;
        try {
            nets = NetworkInterface.getNetworkInterfaces();
        } catch (SocketException ex) {
            ex.printStackTrace();
        }
        for (NetworkInterface netint : Collections.list(nets)) {
            for (InterfaceAddress address : netint.getInterfaceAddresses()) {
                // *** Exception would occur on the next line when
                // *** address.getAddress() would return null
                byte[] addr = address.getAddress().getAddress();
                if (addr.length == 4 && addr[0] != 127) {
                    int prefixlen = address.getNetworkPrefixLength();
                    int maskval = -1 << (32 - prefixlen);
                    IPAddress mask = new IPAddress(maskval);
                    //my_netmask = mask;
                    System.out.println("Netmask   = " + mask);

                    IPAddress myip = new IPAddress(addr);
                    //my_ip_address = myip;
                    System.out.println("Local IP  = " + myip);

                    IPAddress broadcast = IPAddress.getBroadcast(mask, myip);
                    System.out.println("Broadcast = " + broadcast);

                    my_networks.add(new Network(broadcast, mask, myip));

                    System.out.print(address.getAddress().getAddress().length + " ");
                    System.out.print(address.getAddress() + " ");
                    System.out.print(address.getAddress().getHostAddress() + " ");
                    System.out.println(address.getNetworkPrefixLength());
                }
            }
        }
    }

    static private void setupNetwork() {
        System.setProperty("java.net.preferIPv4Stack","true");

        enumerateNetworks();

        // ... stuff that would happen after the exception
    }

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {}

        setupNetwork();

        // ... stuff that would happen after the exception
    }
}