How do I get MAC address of a access point using java code?

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Java

Hi, I'm a java beginner and I would like help to solve my problem. I want to use java language to detect an access point and display the mac address of the access point. I have 3 classes and can only detect ip address and mac address of a host. Below is my code.

head.java
public class head
{
    public static void main(String[] args) throws InterruptedException
    {
        String tracerserver="http://127.0.0.1/eds/track.php";//tracker server address
        int timeRange=1;//in minutes

        System.out.println("Application running now...!");

        while(true)
        {
            try
            {
                tracer machine = new tracer();
                //System.out.println("Ip address: "+machine.ipaddr());
                //System.out.println("Mac Address: "+machine.macAddr());

                String requestParameters ="ip="+machine.ipaddr()+"&mac="+machine.macAddr()+"&point=3.223,2.93";
                sender.sendGetRequest(tracerserver, requestParameters);

                Thread.sleep((timeRange*60000));
            }
            catch(Throwable t)
            {
                System.err.println("Error:"+t);
            }
        }
    }
}

sender.java
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.*;
public class sender
{
    public sender(){}

    public static String sendGetRequest(String endpoint, String requestParameters)
    {
        String result = null;
        if (endpoint.startsWith("http://"))
        {
            //Send a GET request to the servlet
            try
            {
                String urlStr = endpoint;
                if (requestParameters != null && requestParameters.length () > 0)
                {
                    urlStr += "?" + requestParameters;
                }
                URL url = new URL(urlStr);
                URLConnection conn = url.openConnection ();
                // Get the response
                BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                StringBuffer sb = new StringBuffer();
                String line;
                while ((line = rd.readLine()) != null)
                {
                    sb.append(line);
                }
                rd.close();
                result = sb.toString();
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
        return result;
    }
}

tracer.java
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.UnknownHostException;
import com.sun.org.apache.xerces.internal.impl.dv.util.HexBin;
public class tracer
{
    public tracer(){}
    public String ipaddr()
    {
        try
        {
            InetAddress localaddr = InetAddress.getLocalHost();
            return  localaddr.getHostAddress();
        }
        catch(UnknownHostException e)
        {
            return "Can't detect localhost : " + e;
        }
    }

    public String macAddr()
    {
        try
        {
            InetAddress address = InetAddress.getLocalHost();
            NetworkInterface ni = NetworkInterface.getByInetAddress(address);
            if (ni != null)
            {
                byte[] mac = ni.getHardwareAddress();
                if (mac != null)
                {
                    String aa = HexBin.encode(mac) ;
                    String ab = "";
                    int a=0;
                    int b=2;

                    for (int i = 0; i < mac.length; i++)
                    {
                        ab+=aa.substring(a, b)+ ((i < mac.length - 1) ? "-" : "") ;
                        a=a+2;
                        b=b+2;
                    }
                    return ab;
                }
                else
                {
                    return "Address doesn't exist or is not accessible.";
                }
            }
            else
            {
                return "Network Interface for the specified address is not found.";
            }
        }
        catch (UnknownHostException e)
        {
            e.printStackTrace();
        }
        catch (SocketException e)
        {
            e.printStackTrace();
        }
        return null;
    }
}

Hope that somebody help me in this problem.