Help needed for a port scanning project

Question

Thank you first.
This is actually my shcool project. we are writing a little port scanner in Java. I want to know how to
tell the OS of a target machine.
tell the UDP and TCP ports( which are UDP ports and which are TCP ports).
My understanding of telling UDP or TCP ports is that an active UDP ports will not respond and a closed one will generate an error.
Thank you again for your advice.

Answer 1

this is the just an idea
echo, 7
ftp-data, 20
ftp, 21
telnet, 23
smtp, 25
time, 37
name, 42
bootp, 67
tftp, 69
finger, 79
http, 79
pop3, 110
nntp, 119
login, 513
printer, 515
route, 520
String cIP = "192.168.0.1";
int nPort = 23;
Socket test = new Socket( cIP, nPort );
public Socket(String host, int port) throws UnknownHostException, IOException{
this(InetAddress.getByName(host), port, null, 0, true);
try{
// connection code in here
catch(Throwable e){}
String cIP = "192.168.0.";
int nPort = 23;
for( int nClassC=0; nClassC<=255; nClassC++ ){
try {
Socket test = new Socket( cIP+nClassC, nPort );
test.close();
} catch ( Throwable e ) {}
public class checkSingleIP extends Thread{
private String cIP;
private int nPort;
public checkSingleIP(String cIP, int nPort ){
this.cIP = cIP;
this.nPort = nPort;
public void run(){
try {
Socket test = new Socket( cIP, nPort );
System.out.println( nPort +" disponibile" );
test.close();
catch ( Throwable e ) {
System.out.println( nPort +" NON disponibile" );
checkSingleIP ip =
new checkSingleIP( "192.168.0.1", 23 );
ip.start();