Java : port scanner (multithread)

import java.io.IOException;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class PScan {

    protected final static int MAX_PORTS = (int)Character.MAX_VALUE;
    protected static InetAddress TARGET;
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        String host = (args.length == 1)? args[0] : "localhost";
        try{
            TARGET = Inet4Address.getByName(host);
        }catch(UnknownHostException uh){
            System.out.println("Unknow Host --> "+host);
            System.exit(-1);
        }
        ExecutorService exs = 
                Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() + 1);
        System.out.println("Scanning host " + TARGET.getHostAddress());
        for(int i = 1; i <= MAX_PORTS; i++){
            exs.submit(new Scan(i));
        }
        exs.shutdown();
    }
}
class Scan implements Runnable{
    
    private int port_number;
    
    public Scan(int pn){this.port_number = pn;}
    
    public void run(){
        Socket sock = null;
        try{
            sock = new Socket(PScan.TARGET, port_number);
            System.out.println("The port "+port_number+" is open");
        }catch(IOException ioe){
            
        }
        if(port_number == PScan.MAX_PORTS){
            System.out.println("Last port reached");
        }
    }
}